Security charms are the most common, but there are quite a few university pranks. I knew of someone who used to make the shoes of romantic rivals shrink half a size on the dance floor, so that he could cut in when they gave up in agony.
There was also a fad for young ladies' slippers to produce the chime of bells with every step. I believe it was meant to convey a winsome, innocent air, but it grew tiresome quickly.