Transpoders - Let them know you are using them for the Power Racing Series. It will be a kit you need to assemble. (Just some LEDs and battery connector to solder on.)
Duracell Procell 9 Volt Batteries,12 count pack of 2 - Multiply the number of cars times two for a two day event, and then get a few more. We give each car one battery each day. Note that Orlando has used rechargeable 9 volt batteries.)