I had a long bed pickup with a fiberglass bed cover. I had a six inch thick foam pad in the bed for emergency camping. With the cold weather sleeping bag I would have been fine for just part of a day.
Might want to re-think that strategy if you're caught still on the highway.
I always carry complete survival gear including food and water for 3 days.
The gear includes Mickey Mouse boots (military surplus), a winter sleeping bag, a tent from the Oz folks that you just remove from its' container and toss it up, it's ready to occupy in 3 seconds, a snowmobile suit, and a whole lot of other stuff.
The reason for the tent is so if I'm stuck while still on the road, I can be comfortably tenting out in the woods nearby, so I'll hear the crashing sound when the snowplow eventually destroys my Jeep.
I don't want to be in the Jeep at that time.