The content for this post came from an Expedition Overland podcast. I found much of it very useful for surviving cold conditions so though I would pass it along in condensed form. If you ever wanted to know more about overlanding, XOverland is the podcast you should listen to.
In this post I am defining “cold conditions” as -30F and colder but some of this is good for warmer conditions.
When packing for a cold weather trip consider that for every 1,000 feet in elevation gained you should plan for the temperature to be 3-5 degrees (F) colder than the surrounding flat land.
Staying Warm at Night: Sleeping bags are rated for survival not comfort. To be comfortable, get a bag rated for around 20 degrees colder than you think you will need. If you can't get or don't want to spend the extra money on multiple bags. You can double up your bags.
Two sleeping bags are warmer than one. But don't put one inside the other. Instead use one as a quilt over the other. If you put one inside the other, zipped up, it will reduce the loft of both making you colder. If you have a wool blanket put it in your bag not on your bag to maintain the loft of your down. Or depending on your sleeping mat, the wool blanket might keep you warmer under your sleeping bag rather than on top. You can also wear warm clothes to bed or get a bag liner. Just make sure that anything you sleep in stays as fluffy as the manufacturer intended.
From my experience, don’t overdress for sleeping. If you sweat in your bag you will be colder and have to deal with a damp bag.
Don’t sleep on a cot. The cot has air under it and little or no insulation so the part of you against the cot will never get warm.
Never breathe inside your sleeping bag. Your breath has moisture, which will make your bag damp. After several days it might even be wet. The wet bag will not keep you warm but now you will also have to think about mold. Consider that in 8 hours, you can exhale 0.5 -1 liter of water. (Correction: This volume of water exhaled in 24 hours not 8.) If several people are sleeping inside an enclosed space, each one is exhaling water making the inside of your tent/RV wet. To combat this, in the morning, turn your heater on and open all the vents and windows to dry everything out before packing up.
Three things you should take to bed with you. 1) Place a water bottle (Nalgene or similar) with hot water in your sleeping bag 15-20 minutes before you go to bed. Remember to check for leaks before you place the bottle in your bag.
2) Take some food to bed with you. Around 5:00 am your body will run out of easily accessed energy which will make you cold. Eat something low in liquids, like a granola bar, or a few scoops of peanut butter. This will give you extra calories to warm you up in about 10 minutes.
3) When you're packing for your trip take a bottle specifically to urinate in so you don't have to get out of the tent during the night. This is also good for avoiding animals during the night. Women don’t forget to practice outside the tent. You don’t want to miss the bottle in a tent.
Food/Cooking: Eat small meals of hot food often. This should be substantial food like soups. Coffee and tea will warm you for a short time, but you need calories as well to get optimum results from this technique.
Consider cooking on your campfire to get double duty from your fuel and not have to leave the fire while you cook.
Take small containers of water. They are easier to thaw or stash inside your vehicle.
Not all fuel burns the same. Cold propane is harder to keep burning. Isobutane is slightly better but they make two blends a regular and a winter blend. Check your container when you’re packing to ensure you have the correct one for your conditions. White gas is the best fuel for winter.