I have fond memories of playing D&D in the barracks with my fellow "volunteers" during US Army basic training. For those not aware, the conditions for enlistees are very similar to prison. We made a d20 out of wadded up toilet paper and a sharpie that had to be kept hidden until late at night. Our "rulebook" consisted of the hazy memory of our DM who had memorized most of 5E (He also had a separate project going at the time of writing down word for word the entire script of LOTR: Return of the King in a notebook, from memory, to pass the time.). It's one of the few things that kept me sane during that time.