Where in the world do you get dry ice? Try searching http://dryicedirectory.com for a location near you.
Step 1: Watch the Video!
Step 2: Impossible Candle Relight
Carefully pour some crushed dry-ice, down around the base of the candle. And within just a few seconds, you'll notice the flame goes out, and the gas turns completely invisible.
Now challenge one of your friends to try and re-light the candle inside the glass. They won't be able to do it and they'll have no idea why.
Even after multiple attempts, the flame goes out every time.
Now simply blow into the top of the glass to push the gas out, and show your friends, that it really isn't that difficult after all. The candle with relight easily
Step 3: Self Inflating Party Balloons
Carefully place one or two of the pieces inside of a balloon, and tie it off. You'll notice the balloon begins to inflate all by itself.
Now try doing this with a bunch of other balloons and throw them all into a basket.
Over the course of about 25 minutes, the balloons will keep growing, until you've got a basket overflowing.
Step 4: Ziploc Poppers
Now seal the bag so it's completely air-tight, and find a place to hide it.
After a minute or two, the bag will be completely pressurized and ready to explode.
It will make an impressive "Bang!" Who could you scare with this?
Now this is completely safe, and you can do it with heavy duty freezer bags as well. The plastic is a little thicker, so a bit more pressure can build before they go off.
Step 5: Squealing Spoons and Shivering Quarters
It lets out an awful squeal, and people will beg you to stop.
You can make a quarter scream the same way. Just lay it flat on the ice, and press down into it.
By the way, It's probably a good idea to use gloves, because these get very cold very quickly.
For a bonus trick, try sticking the quarter in sideways. It'll start shaking uncontrollably.
Step 6: Levitating Bubbles
Now wait for the gas to fill it up, and turn invisible.
At this point, try blowing the biggest bubble you can, and drop it right in the center.
Instead of popping on the bottom, it levitates around in mid-air, and will make your friends wonder, "what kind of sorcery is this?"