My car is well-maintained but elderly in terms of years and miles. I was on my way to an appointment when I saw the hood starting to rattle around at highway speed.
Like every other car I've seen, my car's hood has one latch that is released from inside and one that is released from outside. You want both to be latched -- if the hood opens at speed you could have a bad day.
When I stopped the car, I couldn't get the hood to latch all the way down. Investigation seemed to indicate that the mechanism was a bit bent, and the "inside" latch was frozen because of that. My kit includes a pair of large adjustable pliers. Some judicious bending of the latch mechanism and I was back on my way in minutes, hood secured.
I understand if you don't want your kit to be too heavy, but it's easy enough for me to have a car kit covering a wide range of contingencies, as long as I'm willing to dump anything I don't think I'll need if I need to carry it a long way on foot.