One of my favorite tricks from years of winter backpacking to have a good warrrrrm night's sleep was to boil extra water in the evening for that last cup of tea. I'd put the extra boiled water in my nalogene water bottle; tighten up the cap; slip it in a wool sock; put it in the foot of my sleeping bag and loosely roll up the sleeping bag. After having the tea and a couple of fire side stories, I'd unroll the sleeping bag and climb inside. I'd keep the sock covered water bottle down at my feet and I'd sleep all night long. Even though the water didn't stay super hot all night, it would keep me warm well into the wee hours by which time I had enough body heat to keep me warm till morning. The next morning I'd have a bottle of luke warm water that I could make my morning coffee while watching others trying different techniques of melting their frozen canteens to make breakfast. Needless to say, those non-believers were all boiling extra water the next night............