I just read this entire thread, wow it was a long one. Previously, I had decided against nalgene as a water bottle because of it's weight, however this thread has convinced me to have at least one for night time heating purposes when unexpected temps occur. For anyone who hasn't read the whole thread, platy's have been reported to leak on more than one occasion. Gatorade can't take the heat and warp/melt. Knock off nalgene shrinks and warps. Some have been very happy with metal containers, watch out for painful heat transfer, put it in a cozy or couple of socks.
Years ago I used hot rocks from the campfire (not wet rocks) and wrapped them in a towel. A water bottle that you bring with you seems now to be a better choice and one that I will certainly try.