25 years since my high school graduation and cliched as it sounds I've found I'm most satisfied when I'm trying to make the world a better place for other people. I have a family to care for but when I had more time found a lot of satisfaction volunteering at church and college. Someone else always has it worse than you and you'll never lack for something useful to do if you think about how you can really make a positive difference for someone else.
If you can find something that is related to one your own passions it's double karma. Our local elem schools have a "Girls-On-the-Run" program that gets elem girls on the road running. It's perfect. I get to exercise and meet some really great kids I'm not even related to - they get to exercise - we all win.