Anyone who is familiar with Cub Scouts, Boy Scouts, or Royal Rangers has seen a pinewood derby car before. The Kits typically include a block of wood, 4 wheels and 4 metal axles or 2 pieces of dowlrod and 4 screws. Chuck most of that because you only need a couple of the wheels and the axles.
Hot Glue Gun
Pinewood Derby Car Kit (optional)
Gears (if motor is not geared)
2 Tires with grip for back wheels
2 Bumper Switches (get at least one with the small wheel on it to use on the bottom)
4 AA Batteries with a holder