Tools! Always are a must and personally think all vehicles should carry them...Spanners and adjustables, screwdriver set, 1/2" socket set and breaker bar, Allen/hex keys, hammer, pointy, stubby and vice pliers, pry bar probably missed a few good ones but that's all I would need to fix my rig anywhere
.. Spare parts are also a good thing too carry like radiator hoses, hose clamps, radiator cap, thermostat even, coolant, engine oil, small arrangement of nuts and bolts if ya keen even stuff like rope, fencing wire, elec wire/terminal kit, tape, radiator stop leak(Never use Chemiweld) and my favorite quick-steel/kneed-it for fuel tank leaks, welsh plugs and busted radiators it does just about anything.
What I have listed should just about set anyone up too be a Bush mechanic!
See one too many backpackers and traveler's come into work with cooked and broken vehicles trying too find something to fix it cause they never bothered too put any maintenance or even have any preparation for the worse and hoped that their $500 Gumtree special was going too make it across Australia with no issues.
Cody