I wrote a post on this a couple of years ago you might find interesting. Basically, my fellow volunteering enthusiasts and I decided it's useful to consider what you're looking to get out of volunteering (are you looking to do as much good as possible? or do you want to unwind and meet new people while doing a bit of good?). Then we suggested you come up with as many different possibilities as you can and rate then based on your priorities.

https://forum.effectivealtruism.org/posts/ScLHyCY6JCr5FtuiY/effective-volunteering

Even if local volunteer opportunities are limited, you might still be able to find one that helps you learn a lot about an issue with EA relevance, or about nonprofit organizations more generally. Some of the benefits which someone could get from volunteer work in the developed world:

• Working with many different kinds of people. For example, volunteering in a free health clinic might help you better understand the experiences of recent immigrants and of people who don't have homes. While there are differences between, say, recent immigrants to the U.S. and refugees in Uganda, getting a better sense for the breadth of human experience could still be useful in your later work.
  • This doesn't just apply to the recipients of whatever help you provide. If you work alongside people with a lot of experience in fields like social work, and especially if you ask polite questions about what they've learned from their education and their nonprofit work, you'll get a sense for different approaches (both practical and academic) to universal issues like poverty.
• Being involved with an organization that isn't trying to make a profit. Nonprofits, whether driven by EA principles or not, have certain things in common (legal structure, the need to fundraise, serving "users" who aren't customers and who may not give as much direct feedback because they don't have a choice of what service to use, etc.) 
  • If you're helping out with accounting, event logistics, fundraising, or communications (to give a few examples), you're probably learning things that could serve you well in a future EA role. I know of several EA org employees who came from the nonprofit world and brought useful skills with them.

If you do volunteer, I'd recommend trying to consider what you can learn from the opportunity. This could mean finding an organization that seems to be unusually effective at doing whatever they do, even if their "cause area" isn't especially promising. It could also mean finding an organization that badly needs more people and isn't particularly well-run, if that puts you in a position to have a lot of responsibility early on. (Of course, I don't advise taking a high-responsibility position if you don't think your contributions will be counterfactually positive.)