I started keeping a small drawstring bag in my trunk with backup essentials: socks, a toothbrush, a phone charger, a tiny first-aid kit, and a small blanket. It has saved me (and a few friends) multiple times when unexpected travel or minor emergencies popped up. Having a mini “just in case” kit can turn a potential disaster into a mild inconvenience.
I carry some tablet compressed towels even in my bicycle kit. These are the biggest kindness you can buy for yourself. When you are going through a tough mess, the ability to wipe off your hands at the end really makes a difference. You'll need a small bottle of water, but in a real pinch, window washer fluid is just methanol and water mixed 50:50... so basically hand cleaner.
Get a small roll of tie wire. This can be used to secure anything in a pinch. In auto racing and aircraft, almost everything that is fastened has extra holes that have tie wire run through them. If you were in a cataclysmic emergency, this stuff can be super handy for keeping the zombies out, to tying them to the roof. Or, ya know, like, securing awkward furniture for transport or holding the bumper cover on after you misjudged how close that post was at the gas station. It can also be used as a hose clamp in a pinch.
Add a cheap small multi tool to your kit to fix the basics and cut said tie wire. If you carry more than one or two keys, get the tiniest flashlight possible. Before I was disabled, I had one like the pic that also had a small knife. Always carrying a light and a small knife saved me more time than I ever imagined beforehand.