Cars - For Car Enthusiasts

Dashcam was a damned good suggestion. I'll add first aid kit, blankets (if you get cold weather), and signal devices like road flares, reflective signage or small traffic cones. Maybe a few bottles of water and calorie-dense snacks. Just remember to consume and replace them periodically.

I keep a bunch of tools on hand because of work but tools are usually one of those things you accumulate over time as they become needed. A good start would be a socket set and a bit driver. Maybe add a breaker bar and a "stubby" driver or 1/4" ratchet for tight places. 1/4" "security bit" sets usually have some flatheads, PH1-3, plus a range of hex and torx bits with the little dimple because "security." A bit driver handled all the fasteners when I replaced my tailgate handle and my interior passenger door handle.

A tow rope and jumper cables are both things that others can use to help you should they not have their own. I know I like it when the person I'm jumping has their own cables ready. My own are usually buried in the compartment under my rear bench, which itself is often buried under toolbags and such. I also keep a couple square-ish off cuts of 2x6 in the bed which make good platforms for a jack/jack stands. You don't usually get to pick where or when you're forced to change a tire and jacks tend to sink and lean in soft earth without any support to spread the weight.

EDIT It's a real late edit but I still don't see it mentioned and it reminded me of something else too.

Thing the first: Fire extinguisher.

Thing the second: Some sort of mounting bracket it for it. Some will attach to a pillar, others might be made to reuse the bolts at the front of your seat mount. Wherever your fire extinguisher goes, it needs to be secured. Same goes for tools and other items which could become projectiles in the event of a collision.