Change your S-belt / belts TODAY and put your used ones in your vehicle as emergency spares.
Cooling system hoses, clamps, and related hose repair kits / methods.
bronzeseal, alumnaseal, some form of radiator stop leak / sealant.
vehicle fluids, oil, water, trans, hydraulic.
toolkit.
ground tarp for rolling around in the dirt / mud trying to fix things.
duct tape. bailing wire. various hose clamps. sturdy big zip ties. large and small ViseGrips.
disposable gloves, as well as work gloves.
A BFH. A 3-lb maul will do.
Appropriate jack and whatever additions you need to change a tire in off-road terrain.
Emergency set of relays and fuzes for your vehicle.
Set of bulbs for your vehicle and the tools to get at and change them.
I carry that crap and a lot more in my vehicles, all the time. Lot of recovery gear, roadside emergency stuff, flares, additional tools, OBDII reader, some comfort items and calories, first aid kit, and weather / season appropriate outer gear. The further away from home or off paved roads I intend to go, the more I carry.