I’d write software and books. Open source software, and probably mostly technical books.
I could be wrong, but I think my code is better than a lot of the open source stuff, and there are endless places where the available code could use major improvement. Just simple things, like a decent desktop RPN calculator for KDE, a working replacement for fetchmail, and so on.
Technical books, because documentation is the other problem with open source. A lot of it is awful, and that’s when it exists at all.
Sure, there are sexier fantasy careers, like rock star or brain surgeon. But I’d be improving the world in a modest way, doing something which I know I can do well.
Why don’t I? Because for the forseeable future I’m going to need a steady income. I can’t even deal with the “work six months, take six months off” plan, because I’d die from the stress.