In all seriousness, I knew a guy who took a soap-stone with him while backpacking and would throw it on the fire (wrapped in foil) and heat it up and then throw it in his sleeping bag. He said it would keep him warm for most of the night. They are supposed to retain temp for a long time.
Presumably. They can also be used to keep drinks warm. I actually didn't get to try them last night. I have my days and nights pretty screwed up and I passed out about 8PM before I ever cracked open the bottle.... and now here I am up at 4AM with nothing to do.