What would you do to keep yourself sane?

I often wondered how people last in those solitary cells 23 hours a day with only an hour of yard time + shower. The reason why I wonder is because when I'm going through times of hardship and negative emotions, I always imagine myself committing a crime .. that's why I end up thinking of prison.

I think I would talk to myself and fabricate different fantasies in my head. I'm not sure how the "library" system works in prison, but I'd try to read big, big books. I'd workout and sleep as much as possible too. It scares the crap outta me knowing that there's only a bunk bed and a toilet there for you all day though.