For you, sleeping bags, tea candles, and hand warmers, snow boots and old ski bibbs and a cell phone charger should be the core for what you need. Add a fleece blanket for each bag if you have the space. (a fleece blanket inside of an inadequate sleeping is a very nice addition.
If you keep a supply of hand warmers then you can add one or two to the bag every 8 to twelve hours to greatly increase it's warmth, and since you will only be keeping old or cheap bags in the car then putting the fleece blanket and the handwarmers inside the bag will get you through the night if you can't run the car heater.
Buying some old ski bibbs from the thrift shop and stuffing them under your seat sure is nice if you have to walk and you left the house wearing cotton jeans or a pant suit.
Last time I had to grab the bag and go was last year. We had torrential rain for what seemed like days. You could actually see the water rising. I have 3 ponds on my property, and when I saw the water rising up to my house, which I thought would never happen, I grabbed my bag, my top shelf guns, some ammo, the boys and took off in the truck.
The road leading to my house is gravel. Up the road, my neighbors pond was spilling over the levy and rushing down the road. It was creepy. I saw fish swimming and flopping on the road. When I hit pavement and went for a ways, the water was spilling over a small bridge. We headed for the church and as soon as we got there the rain stopped. When we were finally able go back home the small bridge was washed out and we had to take a 5 mile detour.
I didn’t use much from bag but it was good to have it anyways.