Contribute to the FOSS projects that you use personally, here you know best why it's important, how it works, and what can be improved. Start by reviewing the pull requests of other contributors to be useful instantly and learn your way around the code base. Then find an open issues that's in your interest and skill range, propose a solution, incorporate feedback, and deliver a pull request. Do that for a while, and if you're actually useful, then someone is likely to toss you some sats.
Indeed! It has given me great pleasure to have contributed in to libsodium, unbound, dnscrypt-wrapper, the Linux kernel, netflilter, and now: datum_gateway. I see this software used in my products that my employer buys off the shelf sometimes. No sats for that yet, but pleasure alone is why I tinker with things I get to use. I remember on LKML a guy once wrote that he cleaned up ... a Makefile in Linux. He then said he's proud he can tell his kids that some CGI animated kids movies was made by artists using Linux (I don't know, Blender?) and that he had a tiny part in the making things used to create that movie. See, I remember that guy :-)
In light of recent arrests, how important is it for developers to remain anonymous? FOSSA
It's all about layers of defense, and cost-benefit analysis. It also depends on what type of work is your calling. Starting a fresh nym is at least a fun experiment, so why not try.
Also: test, publish reviews, guides, manuals, design navigation flows, visuals, backup copies, suggest improvement, update documentation, advertise and so on (beside coding).