Edit 2023 February: Amazon is shutting down their "Amazon Smile" program later this month and this post is no longer relevant.
Action: Click this link . Scroll to where it says "Or pick your own charitable organization". Type in a charity you like, such as the Against Malaria Foundation. Hit "search", and select the charity from the list. In the future, when you use Amazon, use the URL smile.amazon.com rather than the plain URL (you can bookmark this page or set up an automatic redirect using a browser extension ). Impact: A portion of the profit from your future Amazon purchases (around 0.5%) will be donated to the charity you chose.
More explanation: Amazon always donates a portion of profits made through smile.amazon.com to a charity, but their suggested charities are ones I haven't heard of in my limited time in the EA sphere, which on a very loose heuristic I take to mean they likely aren't as good as the classics. Before switching to the Against Malaria Foundation, my chosen charity had been Pencils of Promise. Amazon's information page on this program says that this was a choice I made the first time I used the smile.amazon.com link. I'm sure that's true, but I don't remember making that choice, and in fact I didn't realize until now that I could change what charity the donations went to. Even after discovering that I could change it, I very nearly didn't notice that I could choose any charity I wanted. I figure I'll probably spend hundred or maybe a few thousand dollars on Amazon purchases in the future, so this should cash out to several dollars or tens of dollars for a few minutes of effort, for an hourly rate of $60-$600/hr.