Astounding class 1 practical joke effects can be obtained with frozen shaving cream.  Freeze a can by immersing it in liquid nitrogen.  Your home freezer doesn't get nearly cold enough, but liquid nitrogen is common in many physics laboratories.  Or you can try "Cryogenics" in the Yellow Pages.  Once the shaving cream is frozen solid the can is peeled off (wear a face mask and gloves), leaving a cylinder of solid compressed foam.  If you try to peel the can off before the foam is frozen, there'll be a "whoosh" noise and suddenly you'll be looking like Frosty the Snowman.

    When the foam thaws, it expands to dozens of times the volume.  Five cans of frozen shaving cream are enough to fill and lightly pressurize a compact car.  I learned of this trick from a friend-of-a-friend who actually did it.  I still visit him from time to time in Folsom prison.