That sounds like a fun place to work!... I worked at a resturant once and we had the best time pranking new employees. Here are a few of the things we would do..
*We would tell the new employee that we needed him to go to the resurant next door and get the bacon strecher... or the mop trimmer, or a can of A.I.R, or a bucket of steam! And we would always make sure the would ask for a manager. There faces were always priceless when they returned, and it was funny when the resturant next door would send their new employees to us for those non existent items as well
*We would have a new employee empty the hot water out of the coffee machine. (it is a continous flow, there is no way anyone could empty it) But we never let them get farther than a five gallon bucket full.
*I would always put lemon wedges on the sholders of other employees. They would walk around with a little yellow friend on their shoulder and most the time would not notice it until one of the guest asked why they had a lemon on their shoulder.
I always had to be careful who I did these things to, you never know who might get offended by a lemon!! However I know for a fact our staff made it through many stressful, busy nights because we were always having a good time and joking aroung with eachother.