I have three vehicles... I normally bash within 15 minutes of my house, so I don't carry much for parts. I do carry my nut/bolt box though, tools, a small box of parts for the savage (axle parts).
If I break something, I drive a different vehicle... if I break 2 vehicles, I go home, because I'm just being retarded with the things I'm trying to jump over/through.
I do carry spare glow plugs, my tool bag (metric wrenches, buggy 4-way, normal 4-way, temp gauge, pliers, threadlock), spare body clips, two glow heaters, spare sub-c for heater, normal duracell C's for other heater in case I forgot to charge the sub-c's..., fuel, bug spray, sunscreen, paper towels, gloves.