Find out the forecast temperatures and make sure you have a suitable sleeping bag for the coldest nights, make sure you have a hat; multiple layers are warmer than one thick sweatshirt. Emergency silver "blankets" are a good precaution.
Really, you just need to make sure that you bring things with you that will keep you warm. Heavy jackets, sleeping bags, boots (if it's going to snow), and things of that nature.
First, know that you are going to be cold. Second, know that you are going to be COLD. Therefore, bring twice as much food as you would in the summer as your body will need the calories to keep your core temperature up.
It is most important to ensure that your feet stay warm, always have fresh warm socks on hand. Cold feet are worse than anything else as it is harder for your body to warm them.
