If you're extra good in prison, you might earn yourself some Spork privileges. No more eating pudding with the folded up lid for you; you've earned the right to use utensils, son! But that's only if you keep your nose clean, stay out of trouble and generally go out of your way to make prison life more bearable for all. So how good do you have to be to earn gun-building rights? You can ask David Marshall Williams that question, he spent most of his prison time building, testing and refining new types of machine guns.
This one caught my eye, but the others are interesting too.