This year, my son decided to build a "Dukes of Hazard" inspired HMMWV (Humvee). These steps can be used to make any number of vehicles.
Disclaimer: The use of power tools in tales certain inherent risks. Proper protective equipment should always be used and tools should be properly maintained. Children should be closely monitored and aided if they are to use any power tools. I am not responsible for any injury you may sustain.
Step 1: Materials, supplies, and tools
1 pinewood derby kit
additional wood (we used balsa, so as to minimize additional weight)
wood filler (sandable)
sand paper (we used 120 and 220 grit dry, and 320 and 600 grit wet)
masking or painters tape
saw (a band saw works great)
power sander (optional)
Dremel tool (optional, but very helpful).