Liquid nitrogen is an endless source of fun. You can freeze things and smash things into pieces. Or you could pour it onto things and then watch the smoke monster move around and then smash things into pieces. Or you could dunk things in it and then watch the smoke disappear and then smash things into pieces. You get the point.
Here’s something else you can do with liquid nitrogen that doesn’t involve as much smashing: pour it on top of gasoline and watch it dance around in curious patterns. Cars and Water dumped liquid nitrogen on petrol, isopropyl alcohol, and water to show the different reactions. My favourite is easily petrol.