My normal kit is a set of screwdrivers, a set of wrenches, a small selection of sockets, a couple pairs of pliers, a wire stripper/crimper, a collection of terminals (spade/bullet/butt), some electrical wire, electrical tape, aluminum tape, zip ties, RTV, a tire patch kit, and baling wire.
I also like to keep a quart of oil, a couple bottles of water, some emergency food, and a couple space blankets just in case of emergencies.
I would look at that list and say it seems like a bit much, but I have used all of them at one time or another.
Years ago when I was working at China Lake, I went out to the parking lot over lunch and found a kid (probably early 20s, but a kid to me) with his hood up just staring at his engine. Long story short, I ended up grabbing my tool kit and when he saw it, he asked if it was really worth it to carry all that around with me.
I responded by asking him if it was worth being able to get back on the road without having to call a tow truck. He wasn't sure what to think of that question.
Edit: my current kit is stored in one of these:
https://www.homedepot.com/p/Husky-12-in-4-Pocket-Zippered-Tool-Bag-HD60012-TH/312387481I make sure to have whatever jack/tools are necessary to change the tire on that given vehicle are present too, but those generally have thier own on-board storage.
