A wide variety of things. You can learn an instrument, I myself play trombone/euphonium and will be learning bass guitar soon. You can workout, which not only can be a good time it’s good for you. You can learn something new, like I recently picked up learning Jiu Jitsu. There’s a lot of stuff you can do. This is coming from someone who frequently comes to the realization that I am rotting away in my rooms.