maybe if there were jail crimes one could be 'make a shank/shiv' and from then you can attack other inmates, and if you dont give it to another inmate before your jail time is up its taken away.
or
New items added to the market that have no use until you are inside, i.e. toothbrushes, pens etc then you can do the 'make a weapon' crime.
or
If you have hi intell you can start a riot from the jail crimes.
or
A few npc's around the jail to pass info thats maybe needed to make a whiskey still from an old sock and a coke can.
ok ill shut up now