The most important factor is being in physical shape, having a metabolism which has experienced severe cold so your subconcious system knows how to react to it, and having your body loaded with sufficient and proper fuel.
All the gear in the world is useless once you get soaking wet. Look at those Special Forces who died of exposure on a training exercise in Florida in temperatures of 54 degrees.
You have to keep some gear and clothing dry.
A friend and I got caught in a weather change from 55 degrees to freezing rain and 70 mph winds which shredded our tent. We loaded up and walked out in the dark, descending 4,000 feet in 18 miles that we had covered earlier that day. At one point, my partner had such severe hypothermia that he went blind, and we had to stop and huddle while our clothing froze. When the freezing rain and sleet turned to a warmer drizzle, we got up and made it to an Adirondack, where we shed our wet clothing and got into our dry sleeping bags and warmed up.
I certainly found out what worked and what didn't. If we had both not been in super physical conditioning and had the nuts, dried fruit, and jerky to eat, we could not have kept hiking and generating heat to stay alive.
