I've met people who've been to prison. One of the simplest gambling games they use is a game made with paper balls (often toilet paper).
They basically create balls, three for each person, then throw them at a wall. To win the game, the balls must land as close to the wall as possible. The person with the highest score wins.
They usually gamble on cigarettes, but sometimes they'll also gamble on a pair of shoes or meals.
It's amazing how people invent everything; the human mind is always amazing.