Might not be that bad, there was a case here in Sweden last winter with a man that got trapped in his car for 60 days, with temperatures reaching -28 C.

He apparently survived by eating some snow (and drinking some soda?) but had nothing else to eat. He had a sleeping bag and I guess the snow makes quite good isolation. Not something I'd recommend though, he was lucky to survive and was in a really bad shape when he was found.

( some pictures: http://www.aftonbladet.se/nyheter/article14394731.ab )