Rubber Poppers
The whole point of these toys was to turn them inside out and watch them "pop." After the third time you set one off in math class, it was likely to be confiscated and never seen again. Luckily, they were easy to replace. Advanced popper owners discovered that it was more entertaining to use suction to covertly stick them to friends' bodies.
I remamber that my mum used to take care of mine and my brother's while we were at school.