I don't see this happening to me where I lived, but if I were to prepare for it I'd take a large, bright (safty orange maybe) tarp, 4-8 plastic shoping bags, a good bit of cordage and a knife.. along with the normal winter survival gear I'd take.. then if this Did happen to me I'd dig out of a rear window, Down then Up, not in a straight line (like for an igloo), I'd take the tarp, bags, and cord, and snow-anchor the tarp over the car so it could be seen and keep the TARP clear of snow.. I'd also want to try to make a inch or so hole down to the window on the Other side from the Top as a vent if I had some type of stove I was going to use.. then just keep both windows open.. that should keep you decently warm, safe, and visible.