Voluntarily serving others through time or money is definitely a good way to find some purpose, or at the very least, just not feel so selfish. A good opportunity that I've found that other HN folk might be interested in is donating your time to STEM clubs at public schools, especially those with less advantaged kids. They're usually after school and the one I'm doing is in the Lego robotics competition targeted towards 5th-7th graders.