I always had a portable CD player plugged into the board somewhere, and if enough regular channels were open I liked to put it there so I could send it to the wedges. I'd bring one or two sound effects CDs and between songs play something unusual through the monitors. (If somebody REALLY screwed up their part, I'd play the sound of a toilet flushing, in THEIR mix only.) One time I had the gain up too high and the sound of a fighter plane strafing run just about knocked the drummer off his throne.