Electronics
I have some experience in Electronics, but this page also covers hardware for Computers.
Robot Car
One year in the Pinewood derby, I (With my dad's help) created a Robot themed car. It had blinking eyes-LEDs hooked up to a 555 Timer and run off some coin cells and a 5V regulator. Sadly, the way I implemented the switch still caused it to drain battery power, and by the time we actually raced it, the battery was dead, and we didn't have time to fix it.