Learn a trade of some sort. Mechanic, HVAC, electrical, plumbing are all skills you will use your whole life. Working on your own home/vehicle can be very rewarding in itself not to mention money saved by turning your own wrenches. It's also a decent way to make a living while you figure out what your really passionate about.

Try learning a musical instrument. Hit a pawn shop and get a cheap guitar or whatever your interested in and learn how to play. It's a great creative outlet, and can lead you to some music you normally wouldn't listen to.

Read a book. Any book. Seriously reading is great for your brain.

Learn a language. Duolinguo kinda sucks but it's free and it gets your brain working.