we had the average stink bombs and fire alarms, but a few i was involved with was writing on a white bored in prit stick, then scribbling on the bored in bored marker when the teacher was out the room, so when she came in, she wiped the bored and it got stuck to the glue. we managed that about 4 times in 1 lesson, and she never cottoned on.
another i did was when id just been given a rape alarm, walking down the busiest corridor in my school at the start of lunch, and occasionally setting it off, so everyone was wondering what it was. had the school baffled for ages!
probably have many more!