Already been said, but bring a survival kit in the event you get stranded. This includes water and non-perishable food. All the other suggestions are good, too, such as a shovel, sleeping bag, and don't forget some kitty litter if you find yourself stuck and needing traction.
Obviously make sure your car is in good running condition. This includes all fluids being topped off, wipers in good condition, and a full tank of gas. Common sense goes a long way.