I used to love playing with Dry Ice in my lab... Nothing quite like a cold burn to get your attention back to the job.
My favourite trick was the dry ice in the beaker of water with Universal indicator. The kids can see how sublimation of CO2 can make carbonic acid, then you just add Sodium Hydroxide to make it alkaline again and they can watch it all over. Well until the CO2 is all gone anyway.
I love science, I am such a nerd and I miss my lab...
