I'd think a spare (fullsize) tire and wheel, or better yet, 2 would be handy in case debris were to down one of your tires. From a mechanical standpoint, I'd also suggest a full set of spare belts and maybe hoses and some (eg. enough for a full change) transmission fluid, oil, and other fluids for necessary components of the vehicle like brakes, power steering, etc. if equipped with such, and some basic tools to pull off basic repairs noted above. Also some starting fluid.
For the body, I'd say, on top of what everybody else has suggested like MREs, food, water, gas, etc. is a water purification unit like the military uses. Perhaps a CamelBak to keep on your person as well. Some survival vitamins to keep in your pockets as well if you can't get to food for some reason. The hydration and vitamins would at least keep your body sustained fairly well, given you're not losing blood or sustained a really serious injury. This is mainly for if you're separated from your vehicle or supplies in general.
Also some chains, ropes or straps; or a winch for the vehicle if you can dig it. But mainly ropes and chains. If you go out in the 'cane, it'd be nice to have a lifeline back to the vehicle so you're not swept away with the winds. Auxiliary lights on the vehicle would be handy, as well as portable spotlight.
If you really wanna get into it, perhaps some knee pads and shin guards; as well as heavy duty eye protection if you plan to actually get outside-the-vehicle footage. Eye protection really is a must, like military goggles.
