I would add some gloves to that.

Since many of the problems we encounter on the road are electrical, I'd also strongly suggest a test light and/or DMM, a small flashlight, #400 sandpaper, and a few fuses.

Schematics are also not a bad idea at all, but some vehicles are much simplier than others.

i never leave my garage without a swiss army knive; you can even reapir a Carter BBS with that!

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62 Valiant
62 Lancer

Be careful about carrying toolboxes in the passenger area of a vehicle.
I had a friend in collage that got hurt bad when his car rolled off the road and the toolbox he had inside the car, beat him up badly.

These days, I am pretty paranoid about heavy items loaded into a vehicle. I always keep my spare and jack bolted-down and drive cautiously when I have loose parts (engine block, crank, heads) loaded into our station wagon.

I have seen some wise owners with a small / short toolbox bolted to the inner fenderwell, under the hood.
DD