Phi,
As a fellow Marylander (Frederick), I know what you mean. It took me 2 hours to drive to Baltimore to work this morning. My bag in my truck always has my "car kit" in it, which has stuff like shovel, FAK, emergency blankets, etc. I always make sure a heavy wool blanket is in the vehicles during the winter though. I saw alot of vehicles in the ditches this morning, and waiting around to get pulled out of a ditch can be a pretty cold proposition. Chemical hot packs are small and useful as well.
The main thing you would have to worry about freezing is any water you have stored (I carry fresh everyday to work anyway, so I don't store it in the vehicle). If you do store it, just make sure the container can handle it without rupturing and leaking.
If you drive a truck and want extra weight in the back, take some bags of cat litter or sand for added traction.
The best preparation is probably controlling your speed and not getting into trouble in the first place, which alot of the folks around here seem to forget...
Have fun shovelling...
Greg