Greg, I bring a spare set of hubs, 1/2 shafts with CV's, calipers, rotors, lower control arms, shocks, struts, tranny, and brake pads to the track. I can replace almost an entire front corner (don't carry springs or camber plates) at the track.

I re-use my hubs, but have them magna fluxed to check for cracks, and have new bearings installed every year. All of the spares go on the car over the winter, and the old hubs/bearings and 1/2 shafts get replaced / rebuilt every winter.