Recently, there was a HN post about how volunteering was found to be the best overall solution for depression in young adults. I'm not particularly depressed, but I do live in a foreign country that, while incredibly friendly to expats, is notoriously difficult to make friends in. I started volunteering at a local organization that teaches refugees how to code, and I just have to say that it's been incredibly rewarding already. I've only been to two of their events but the sense of community that you get there is really overwhelming.
The funny thing about this is the work isn't very different from what I'd be doing on a day to day. Code reviews and a little bit of teaching. It's not that I feel I'm doing an especially large amount of good, I think my day-job definitely outpaces the volunteering in terms of net good done in the world. But there is something about community that's incredibly powerful.