Alchoholism.
You should be able to challange other people at tavers/mead halls to drink for gold. The first man to get drunk will lose the battle and lose gold, and your endurance plays a role on how much alchohol you can drink before getting drunk. The playes vision should get blurred, and the player characters should sway when walking and be unable to walk straight. If you get too drunk you will pass out for some hours and if you didnt rented a room, then you will wake op in the streets with a chance to get ill.This also gives us players something to in the nights of the game.
Fellow forum members are welcome to add ideas.