Spare critical parts and fluids. If you can seal them properly:
2 qt ATF
4 qt (or your vehicle capacity) motor oil
4 qt gasoline
1 pt heet/methanol
mini tool kit
Tire plug kit
manual pump
12 vdc pump
12 vdc light
12 vdc fan
39-55 gal garbage bags (think containment, poncho, sleeping bag, etc)
body towels
hand towels
paper towels
isopropyl alcohol
gojo
large first aid kit
Oh yeah, a bigger bag that you actually leave in your vehicle.