My truck has tool boxes that I stock separately from the shop(s). Each has a purpose. The driver's side has all of the hand tools that I regularly need, in stackable boxes. The right side has ratchet straps, tow rope, hitch pins, portable air compressor, and magnetic mount tow lights.
Behind the driver's seat - and THIS is very useful: flares, spare lug nuts, spare caps for axle oil reservoirs, tire valves, valve tool, red cargo flag, big lug wrenches - basically anything that I'll need for towing the trailer in a separate grab and go metal tool box.
