A package of wet wipes for interior spills, cleanups, etc. You make messes in the car when travelling.
I second the tire patch/plug kit and some form of compressed air or nitrogen. I use a tank but an electric air pump is OK, just be sure to test it before you leave as the ones I see are low quality.
You can also use an inflator that screws into a spark plug hole, has a hose long enough to reach the furthest rear tire, and an inflator valve. To use, you pull one plug, fire up the motor, and let the engine pump your tire. Don't overlook the fact you will need the proper spark plug socket and ratchet with the correct extensions etc to actually reach a spark plug (doesn't matter which one).
Yeah, the motor runs a little rough, but not rough enough to stall. It's the kind of high reliability, low technology tool I prefer, because "always works" in my book is better than "probably works, I hope".
Way more robust than the noisy, leaky, dubious reliability electric inflators I usually see for sale. Like I said I carry a 10 gallon tank inflated to 125 psi, but I prefer it for versatility. In a car, with your only need for air being a tire, it's overkill.
Another plus for carrying a full jug of windshield washer fluid, and checking the wiper blades and washer pump before leaving.
You should be carrying your emergency car kit. Have a look to make sure everything is stocked up and useful, versus melted chocolate bars and bandaids glued to the container.
I always carry a small coffee can (or similar, metal can with plastic lid) with a roll of toilet paper (you can remove some to make it fit) and a bottle of hand sanitizer. Of course there is the obvious use, but also in an emergency it makes a useful source of dry fire kindling. Don't be afraid to buy the large refill-sized bottle of sanitizer; it's a very effective fire starter and if you need a fire, well, not having a means to start one in the rain is a big deal.
