Take a toothbrush and rub the handle on concrete/stone/brick until it's a point and you have what's called here a "shank." Pencils, ditto. You can think of other things, because ANYTHING can be made into or used as a weapon.

Get a clean plastic rubbish bag and dump in a can of mixed fruit segments (what we call here "fruit cocktail"). Add a slice or two of bread and some warm water and hide it somewhere warm where the odor won't be noticed, such as in a toilet tank. It will ferment and you can sell it to other inmates.

The human ingenuity for violence and the bad seems to know no bounds.