Spare fuses (small/large, at least 2-3 of each value).
Spare bulbs (for everything, from headlights to marker lights to interior lights).
Unopened container of every type of fluid the car takes (steering/brake/tranny/oil/etc.).
Funnels for said fluids (metal, as I had too many plastic ones turn brittle and disintegrate on contact).
Etc.
Most people who plan at all, plan for The Zombie Apocalypse™, but can be downed by a simple blown fuse.