I was thinking of doing something along the likes of a Warden Jail RP.
Someone of the guard team is chosen as Warden, he gives the orders and if they aren't followed, Guards can kill prisoners.
So if he says that once the cell doors open and you aren't standing at a wall or something, Guards will shoot you.
If the Warden is killed, it's a free-day and everyone gets to do whatever and don't have to follow anyone's orders.
Maybe a bunch of mini-games like Simon says, last reaction or even hide-and-seek.
Last prisoner alive gets a Last Request. He can say "I choose freeday for me and that guy" and they are the only ones to get that freeday in the next round, Wardens can't touch them.
Also small rules like no free-shooting allowed, or camping on a prisoner who didn't do anything just because he's 'suspicious'.
/totally not copying Garry's Mod