Another is lighters. Say you want to light a cigarette, how do you do it in prison? You don't have lighters or matches. So what do you do? Well, there are many different ways of going about doing this. One method is to take two AA batteries, two razor blades from a disposable razor, flip one battery with the negative terminal facing up and the other with the positive terminal facing up, tape one razor blade to the bottom with both batteries separated on the ends of the blade, then take your other razor blade, snap it in half, and tape them to the top of both batteries (optional, you could just touch them together yourself) and bam, you've got a spark! Also remember to always use electrical tape because scotch and duct tape isn't airtight enough.
Pic related was made using a wire taped to the negative terminal and in order to light it, you touch the other end of the wire to the positive terminal, with the exposed wire end heating up/sparking as you touch it in the middle. There are countless variations of this that are far simpler, some of them involving graphite in surge protectors.