I drive a lot of highway miles 340,000 in the last 14 years.
Tires are #1, so I have two spares, air tank, air compressor, tire plugs, jack & tire wrench.
Second are spontaneous coolant leaks (cracked plastic radiator tank, hole in a hose) so I have epoxy, hose splices, clamps, tie wraps, and a water jug.
Third is a spare alternator, belt, jumper cables and necessary tools.
This is 99.9% of everything that can go wrong.
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I once had an idler pulley SEIZE at night in a REALLY BAD part of Dallas. (remote, also)
By the Grace of God, I actually had an old one in the back of the truck! But hardly any tools.
I changed it with: a claw hammer, a jack handle, and a channel lock pliers. Miracles never cease.