I've done a winter camps in the past, and it can be a good experience or it can be f'n miserable. Key factor is in how much you plan ahead. I'm by no means an expert, and I'm sure there is plenty that could be added to this so feel free to do so.
In no particular order, the most important things to address are Food, Heat, Shelter, and Clothing.
Food: Due to the fact that your going to be cold to some degree, your body is going to be using up a lot of calories trying to keep itself warm. This means your calorie intake per meal should be more than what your using. Big, hearty, warm meals are the key here. It's also important to stay hydrated, most people wouldn't think it in the winter, but your body needs water regardless to operate right. Warm beverages are a plus, but cold water is better than nothing.
Heat: Your main source of heat will be your camp fire. It's okay to have more fire wood than you think you'll need, it can always be used later, or by the next guy. As a back up small propane heaters work very well. They're easy to use, and you don't have to worry as much about burning the forest down. If you have multiple people try to schedule a rotating fire watch overnight, waking up in the morning and trying to get a fire going sucks.
Shelter: Not much to say here, most everyone has tents. If you have a choice between a larger or smaller one, go large. Chances are it wouldn't need to be staked down (the ground could be frozen.) You'll probably need extra room for larger sleeping bags, blankets, etc. Plus if you need to change clothes, you'd want to do that inside the tent.
Clothing: LOL - Lots Of Layers! A good base layer of long johns/polypros/etc is a must. Build up from there, avoid cotton, prefer wool. My opinion is fleece is a good mid layer. Make sure you have awesome socks, hats, and gloves. Thin glove liners are a plus for when you need to do more delicate tasks without freezing your hands. One overlooked thing is a good neck warmer / scarf /balaclava and one big enough to pull up onto your nose.
Does your BOB at least have: water, basic tools, fire, food, first-aid kit, and shelter?
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