I pretty much keep a "72 hour" kit in my car all the time. There are a couple prior topics that get into lists for that kind of kit pretty well. That means I have signalling, firemaking, flashlights, water, rain/wind gear, 3 days of food rations, FAK, basic gear like sharps, paracord, space blankets, repair stuff, etc. in a day pack all the time.

In the winter, I just add enough fleece or wool pullovers and pants for my family in a duffle bag with some old gloves and hats that we would never wear in public, <img src="/images/graemlins/grin.gif" alt="" /> but, would keep us warm in an emergency. I always have some boots and a parka in the trunk. In that duffle bag I throw a bunch of handwarmers and a couple of those small firestarter logs, (there is firemaking gear in the 72 hour pack, but, I think being able to light one of those little firestarters up might be a real emotional lift for my wife and son if we broke down on some isolated road when we're driving up to a ski place in Maine or New Hampshire).

I think I have enough fleece and wool stuff in there to keep warm, but, maybe a couple wool army blankets wouldn't be a bad addition as was mentioned before.

For communication, I always have a cell phone, but, I also keep a handheld FM amateur radio and a repeater directory in the car. There are plenty of places that the cell phone is dead, but, you can usually find a repeater that you can hit on 2M or 70CM. (Just in case)