For the Game Jam, we put together a game called the dinosaur race. The main concept of the game was to make it to the end of the track before the other person. Both players would roll their dice and the person with the highest number gets to move one spot up. If there is a tie then both players bounce the ping pong ball in trying to get it into the basket. You do this until one person messes up. The loser has to move backwards one spot while the winner gets to stay still.
Creating a game in such a short time was a challenge even for a simple game like ours. We pretty much had to stick to very simple common game mechanics all working towards a goal.