When you are packing for a camping trip in the cold, think about the layering system you will use for your entire body to stay warm and dry. Have a base layer of clothing that will wick away the wet from your skin. The base layer should not be made of cotton as cotton will retain moisture and will not keep you warm. Pack a layer of clothing to act as insulation and an outer shell layer that will protect you from wind or rain. Use a layering system that will keep you dry inside and out and will retain heat.
Clothing for Your Extremities
Pack gloves, mittens, scarves, hats, face masks, etc. Use a layering system for your feet as well. Take care when choosing what material to bring (specifically not cotton) to be sure you will remain warm and dry.
Make sure you have your shelter determined beforehand. Take a tent, tarp, sleeping pad and a sleeping bag that are appropriate for the weather. Make sure your sleeping bag is rated lower than the temperature you expect to be sleeping in.
Pack a headlamp or a flashlight, along with extra batteries, to use as a source for light for when you get up in the middle of the night for a bathroom break, night hiking or just a trip to the car.
Food and Water Supplies
Bring an adequate amount of food and water supplies for any overnight trip. Make sure they are appropriate for cold weather, as some foods freeze. Make sure you are able to start a fire (with matches or a lighter) if you need a heat source to cook food or defrost water. If drinking water is not available, bring water or proper water treatment. Store your food according to regulations of the area you are camping in.
Bring an emergency first-aid kit. Have a map of the area, along with a communication device (such as a whistle, cell phone or satellite messenger), along with important phone numbers for family members and local officials.