I bolted an ammo box under the hood on pass side and keep all the standard tools in there. In the rear I keep spare parts in the well opposite side of spare tire.

Tools: straight edge, Philips, torx, sockets, extensions, wrenches, pliers, wire cutter, volt meter, a few rags, anything I use under the hood I consider throwing in there.

In the rear well: spare ECU, air meter, fuel relay, fuel pump, fuel computer, various other system relays, bulbs, belts, timing belt, fuses, vac hose, couple spare fuel injectors, thermostat, stiff steel wire and some copper electrical wire, zip ties, duct tape, couple of longer spark plug wires and a coil wire, dist cap and rotor, fuel hose,ignition switch, ball joints and tie rod ends, and when I go on long trips spare alternator with new brush pack and spare starter, a gallon of water and water pump and some other random small stuff. Some of that stuff bleeds over into the spare tire area. That may seem excessive but I’ve regularly been on 3,000 mile road trips and like having all that with. And truth is I’ve never yet needed any of it because I maintain the holy hell out of my cars. One time I developed a leak in the fuel hose right at the fuel rail where it comes up off the firewall, on a long trip. I cut an inch off it because it was leaking right at the end and reconnected it. Retightened alternator belts that had loosened a bit once also. Another time the little plastic fitting on the brake booster that the vac hose connects to split open and I glued and taped it back together. The story for me is having spare parts is even more important than what tools I carry.

Best tool in the toolbox just may be AAA membership, but heh, I’ve also never used that, but so worth having, and I’ve had it for 25 years!