I live in an area where the roads will occasionally flood and leave folks stranded so I keep an overnight bag of sorts in my car. Solar blanket, couple lighters, life straw, two MREs, two bottles of water, basic hygiene kit, crank light / charger, first aid kit, pill case (aspirin, caffeine, etc), tarp, cordage, multitool, a paperback, spare change of clothes, a boonie hat, travel towel, and a Hellcat with a spare mag. Figure I could get home with it if S really HTF, but that's not its intention.
Oh and a couple shooters of vodka, either for antiseptic or entertainment. You'd be surprised how boring things get instantly when the lights go out.