A slightly boring answer: I think most people should at least partly read something that overviews common theories and frameworks in normative ethics (and the arguments for and against them) and something that overviews core concepts and principles in economics (e.g. the idea of expected utility, the idea of an externality, supply/demand, the basics of economic growth, the basics of public choice).

In my view, normative ethics and economics together make up a really large portion of the intellectual foundation that EA is built on.

One good book that overviews normative ethics is Shelly Kagan's Normative Ethics, although I haven't read it since college (and I think it has only a tiny amount of coverage of population ethics and animal ethics). One thing I like about it is it focuses on laying out the space of possible ethical views in a sensible way, rather than tracing the history of the field. If I remember correctly, names like Aristotle, Kant, etc. never show up. It's also written in a very conversational style.

One good introductory economics textbook is Tyler Cowen's and Alex Tabarrok's Modern Principles of Economics. I don't know how it stacks up to other intro textbooks, since it's the only one that I've read more than a little of, but it's very readable, has very little math, and emphasizes key concepts and principles. Reading just the foundational chapters in an intro textbook, then the chapters whose topics sound important, can probably get most people a decent portion of the value of reading a full textbook.

While it's hard to disagree that people should be familiar with the basics of economics, statistics, &c. I am not excited by the spirit of the question and the references to 101 materials.

First, I expect research scholars (and forum readers) to have quite a bit of shared knowledge about topics useful for EA. But more importantly, such advice doesn't make use of distributed coordination [1] and doesn't expand our aggregated knowledge. So I would be much more excited for general recommendations with "randomness," which decorrelated the individual decisions.

For example: read a bunch about a few historical periods of your interest. No hurry with that; maybe, don't solely read about the West; maybe, read something by anthropologists or econ historians. Doing so will expand the group's intuitions about social movement, technological development, causes of war/conflict, power &c.

[1] A similar problem arises with a naive interpretation of 80K career advice (before stronger emphasis on personal fit): people would concentrate on the explicitly outlined paths without accounting for others doing the same.

Maybe the top X posts on the EA Forum? Also maybe adjacent things like Top 10 blog posts read by EAs overall,  Top 10 posts on LessWrong, top 5 books, top 5 academic papers etc?

I think reading things already read by many EAs, in addition to being intrinsically useful (presumably the fact that many other EAs read a post is evidence towards it being actually good) is also advantageous for coordination as an intellectual community. For new writing, if you find it safe to assume that (at least for non-introductory posts), 99% of your audience is familiar with Y concept, then you can make more progress compared to worlds where you can only assume that 70% of your audience is familiar with Y. 

(Obviously there is also value in having diversity in thought and knowledge among EAs, but that's less relevant to this question).

I would recommend everyone to read the book How to solve it, by Polya.

It covers basic techniques for solving a problem, from "solve a simpler problem" to "decompose the problem into subproblems". Its examples are high school trigonometric exercises, but the techniques apply much more widely.

I claim that if you understand the lessons in this book (which, granted, takes a lot of practice you will need to get elsewhere) you get 60% of the benefit of having coursed a math major.

[I have split my answer loosely across 'themes' to strike a balance between spamming answers and allowing more fine-grained voting/discussion.]

• Something that has more of a "humanities" flavor and/or helps you understand that perspective rather than triggering "this is just crazy/empty/???" reactions. Maybe some people can get this from Wittgenstein, or from Rorty (e.g. Contingency, Irony, and Solidarity), or from Deirdre McCloskey (e.g. this paper [might be paywalled] or this one) ...
• I also kind of think everyone should read at least one biography, in particular of people who have become scientifically, intellectually, culturally, or politically influential. (Robert Caro's The Power Broker on Robert Moses might be a particularly interesting one but it's also very long ...)
• This one is a bit whacky, but I think there are some important points in Carl Schmitt's The Concept of the Political, specifically how he tries to define 'the political' by saying “the specific political distinction … is that between friend and enemy.” But yeah then he also says a few terrible things.
  • This from the SEP probably gives you a rough idea of what to expect: "Schmitt is often considered to be one of the most important critics of liberalism, parliamentary democracy, and liberal cosmopolitanism. But the value and significance of Schmitt’s work is subject to controversy, mainly due to his intellectual support for and active involvement with National Socialism."

I actually found some notes with other papers I had semi-seriously (cf. OP) tagged as "everyone should read this".

I do think that (at least for me) they all met the bar of "teaching me something interesting about the world, or about how to think, that is useful even if I don't plan to become a specialist in the respective domain". They might require some domain (and maths) knowledge to appreciate, however.

They are definitely not well-prioritized, e.g. heavily skewed toward stuff I was reminded of recently.

• Clauset et al. (2009[2007]), Power-law distributions in empirical data (see also this appendix in Ben Todd and my recent research)
• Stigler & Becker (1977), De gustibus non est disputandum
• Lieber & Press (2017), The New Era of Counterforce
• Hilary Greaves, Discounting for public policy: A survey
  • (Look, sometimes I do like work by EAs!)
• Huemer (2008), In Defence of Repugnance
• Liebowitz & Margolis (1994), Network Externality: An Uncommon Tragedy
• Mordechai et al. (2019), The Justinianic Plague: An inconsequential pandemic?
• Nisbett & Wilson (1977), Telling More Than We Can Know: Verbal Reports on Mental Processes

Here's my guess:
 

At least one (and probably more like 2-3?) reasonable introductions to Bayesian statistics in practice. I got it from Nate Silver's The Signal and the Noise + a Coursera course. I also hear good things about Bayesian Data Analysis by Gelman et al, various writings by Yudkowsky, and various lecture videos online. Students currently in university should also consider taking an introductory class in statistics (though supplementary work needed if it's not Bayesian, which most introductory courses are not).

Some practice is probably also useful.

I suspect the exact material doesn't matter that much here since the core lesson isn't that hard, just that the level of statistical rigor that most EAs casually absorb in the "EA memesphere", while higher than many other places, is nonetheless lower than can be gleaned from an introductory course in Bayesian statistics, and the latter is (I claim) better for the overall culture.

[I have split my answer loosely across 'themes' to strike a balance between spamming answers and allowing more fine-grained voting/discussion.]

• Some basic economic history, a good short thing might be e.g. Luke M's posts on the Industrial Revolution. Or some Our World in Data pages/articles, or I'm sure there are also good academic review articles ...
• Some basic statistics, though idk about a good source.
• Some basic economics, but I probably can't give you a great list of what exactly I would think is important or what good sources are. I think this piece on Coase and externalities has the right flavor but obv doesn't cover everything.
  • Also specifically some of the basics of growth economics. Like know about some basic endogenous growth models and be able to understand, e.g., Nordhaus's "singularity paper".
• Some basic evolutionary biology, like idk maybe The Selfish Gene works (read it >10 years ago so don't remember well).
• Some basic economic theory + empirics on "general purpose technologies" (just look for the papers with most citations on that search term).
• Something on broad trends in technology and/or research, like the Are ideas getting harder to find? or the bottom line of the How predictable is technological progress? paper (ignore all the maths)
  • Maybe also other 'long-term trends', e.g. Pinker's The Better Angels of our Nature.
• Some basics on international relations, but focused on "how should we think about nation states relating to each other at a very high level?" as opposed to more in-the-weeds debates. Again I don't really know of a single good intro, but maybe reading e.g. Mearsheimer's (1994), The False Promise of International Institutions gives you a good sense of some key questions even if you don't agree with its conclusions (can also look at other contributions to that volume of International Organization if you wanted different views). I would include Wendt's (1992) very influential Anarchy is what States Make of it: The Social Construction of Power Politics if I felt it was more on-point and better written ...
  • Maybe also Fearon (1998), Bargaining, Enforcement, and International Cooperation, but I'm not sure how accessible the point which according to me is really important is from just reading the paper is, and I suspect one can also get it from understanding basic economics.

[I have split my answer loosely across 'themes' to strike a balance between spamming answers and allowing more fine-grained voting/discussion.]

• Difficult Conversations: How to Discuss What Matters Most
• Something on the basics of cognitive-behavioral therapy that allows you to do rudimentary self-therapy and 'teach' it to others. [I think this is useful beyond the narrow use case of "treat clinical depression". It also doesn't need to be labelled as CBT, e.g. The Charisma Myth works too for some aspects.]
  • Also just some rudimentary knowledge on common mental health issues, e.g. things like this.
• Similar for other non-epistemic things that might be big deals for people you interact with, like idk "common work-life balance challenges for parents" or "common challenges for Chinese-Western conversations" or whatever. Unfortunately I don't know of great specific sources off the top of my head.

[I have split my answer loosely across 'themes' to strike a balance between spamming answers and allowing more fine-grained voting/discussion.]

• Maybe some basics on how deep learning works and what roughly we can currently do with it. Again, I think this may have the right flavor but probably only works for people with maths background and is quite skewed toward comparing deep learning to the brain.

I feel a bit like "after you've read all of this maybe you can start reading the EA Forum". :) That's obviously not a literal recommendation, but you get the idea.

I would focus on reading key EA content (including cause-specific content, depending on what cause they choose).

E.g. if they're longtermists, I'd say they should read Superintelligence and much of Bostrom's other output, The Precipice, various articles and blog posts on AI timelines, and so on. 

For more general EA concepts and ideas I'd refer them to Doing Good Better, the new Wiki, and/or a few online talks like Owen's "Prospecting for Gold".

Some of the other recommendations in this thread are not as directly related to EA. While I generally like them, they don't seem as key to me as those that I've listed.

The Less Wrong 'Best Textbooks on Every Subject' thread is getting a bit long in the tooth sadly, but is still my starting point when I'm serious about learning a subject: https://www.lesswrong.com/posts/xg3hXCYQPJkwHyik2/the-best-textbooks-on-every-subject

There is an Effective Altruism Books List on Goodreads, suggest more books and vote on the ones that are already on it.