Have any three and four season backpackers or campers tried this hack on those chilly nights when you just can't seem to get warm enough to sleep?
1. Heat water with your stove, it doesn't have to be boiling.
2. Carefully put the water back into your Smartwater bottle or whatever you use (a small funnel helps) and replace the cap.
3. Stuff the warm/hot water bottle into a dry sock, and fold the top over on itself.
4. Snuggle and sleep.
If you're ground camping, this can be done without getting out of your sleeping bag, just like making breakfast inside your tent or vestibule.
Hammock hangers may have more logistical problems to solve, but it might be worth it if you're really chilled.
It's nothing but a modern method of what Scouts, trappers, and even Grandma Gatewood used to do by taking flat rocks warmed by the fire and putting them under the duff and moss they used for a sleeping pad.