Life: continuous learning, whether it be a new language, a new skill, travel. Whatever I learn usually produces benefits in unexpected ways, years down the road.
Runner-up: barbell weight-lifting, three times per week. If you've never been strong, you owe it to yourself to try. You get a physical sense of capacity to match whatever mental sense of capacity you've achieved.
Work: Trying my own thing. I had no clear plan, but I had criteria to evaluate whether what I worked on was paying off.
Two years out, I've got steady monthly passive income, and am working for a startup doing work I'm passionate about (selling an online LSAT course) while continuing to pursue my own projects.
Casting off the set path of law school/a job opened my mind to new possibilities and forced me to find my own way.