The Pinewood Derby is a traditional crafting event among Cub Scouts in the United States. Boys are given a block of wood and some plastic wheels. Their job is to carve and paint the block into a car that, when released at the top of a long ramp, will beat the other similarly made cars to the finish line. When I was a Cub Scout, my Dad showed me how to add weights to the body. Doing so was completely within the rules. Adding CO₂ canisters to the car, however, probably isn't. It's actually a fairly sophisticated modification because the tubes have to open at the right time. A video at the link shows how it's done.

Link via Hack A Day via MArooned | Photo: The Hell Ya Better