I used to carry a lot of spare parts and tools, but I cut back to a pair of channel locks, a crescent wrench, a #2 square screwdriver, a box cutter, an obd2 scanner, and a lug wrench. All the other stuff was dead weight and cut into my towing capacity. For spare parts I carry fuses, hose clamps, crimp connectors, bungee cords, 9v battery in case the co detector beeps, and a tube of dicor. Never needed more than that for field repairs in 10 years or rving. If I take bikes along I add a tire patch kit and pump.