What tools every rig owner should carry

Beyond the obvious (jack, lug wrench, tire gauge), the tools that actually get used most on the road: a good multimeter (cheap ones work fine for basic diagnostics), a basic socket set covering both SAE and metric since rigs mix both, dielectric grease for electrical connections, and a headlamp since you'll inevitably be working in a dark storage compartment at some point. What's already in your kit, and what are you missing?