When I drive in cold foul weather I wear an Alaska-ready parka with integral hood & removable fake fur ruff, long pants (sometimes with fleece lining or long underwear), toque, gloves or mittens, thick/warm socks and hiking boots. I do not just assume I can stay indefinitely inside a heated car that continues to run, no matter what else might happen to me or to the vehicle on the way. I check the local weather predictions twice a day, and make sure the tank is full whenever threatening weather is on the horizon. My local stores never market a suitable parka for local conditions, so I order mine from a Colorado maker that used to supply parkas for the Alaska Highway Patrol.
Spare food, water, sleeping gear is another matter. Before I retired I had to drive over the northern half of my state in any and all weather conditions and times of day as part of my work.