I've submitted PRs and patches to well known projects like Drupal, three.js and Wordpress. Some of them even get merged lol.. Also if I experience a problem and find an open issue I'll add my 2c if I think it's useful. To be honest I think in open source participating in issue comments and lodging quality tickets is as important as writing the code side of things. I have my own open source projects and thoroughly document information I think could be useful for others.

I promote FOSS in my personal and professional life where I can, and try my best to practise what I preach. Recently managed to convinced my financial counsellor from local government to look into LibreOffice which I'm quite chuffed with. They didn't even know free software existed and are excited to tell others small businesses about using it to save money.