One of the things I carry in a vacume sealed bag is INstant Jello that is NOT the sugar free. That give you the sugars, carbs and the nutriance to comabat the sleepy feeling. Muscles twitching and shivering takes a lot of enrgy, and you have to feed that need and contend with the exhaustion that will follow.

From my expeiance taking a dip in the Ocean in Alaska, (sitka) It was the fact that I had fleece on and was able to get out of the watter fast. but I still had a few miles to kayak back to shore. In extreem cold you may and will need to shed the cotton but I have found that flece will evacuate to a damp state very quickly.