You really carry all that crap in the trunk and don't carry a spare?? When was the last time you had all 8 plug wires or spark plugs go bad at the same time? Most of your items I keep in the garage but I don't haul them around. They usually give some sort of warning that they need to be replaced before a complete failure. If some items start to look tired, I replace them before I head out. Regularly maintaining a vehicle is a better bet that carrying all those spare parts with you all the time. The 4 main areas that you don't skimp on....battery, tires, oil changes, and cooling system. If you keep on top of those, the rest seems to give you less trouble.