Dear Folks Unprepared For Extreme Cold:

Here's advice from a former mountain rescue volunteer who's slept comfortably in snow caves:

1. Wear a warm hat, even in bed
2. Wear warm socks, even in bed
3. Wear layers, even etc.
4. Drink warm SWEET liquids (Sugar = metabolic heat)
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5. Fill a bottle with warm water + cuddle it in bed. The same blankets that keep the cold out also will keep that heat in. (Mountaineers often carry a special "pee bottle" to fill then cuddle in the middle of the night: why waste the warmth?)
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6. DON'T use open flames indoors to keep warm! Tents don't have heaters, bec. carbon monoxide kills.
7. Don't be afraid to call for help. Seriously. Sometimes, the environment can kill, and that's what rescuers are FOR!
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Endorsed. The purpose of layering is to trap warm air next to your body (and, when physically active, to enable body temp microadjustments to avoid sweating, which chills). Eight layers of Spandex won't do that. Think "boyfriend sweater." https://twitter.com/piratefoxy/status/1361648659797049349

Also endorsed. We lose heat through radiation (ergo clothes, bedding), conduction (ie touching cold surfaces, so sit on padded furniture + wear socks/slippers indoors), + convection (air currents pulling heat away, so PLUG GAPS + avoid breezes). https://twitter.com/K810Mt/status/1361607387719692288

Agreed. There's a reason climbers carry Goo gel. Also:
1. No caffeine. It makes you colder.
2. No alcohol, for the same reason.
3. Real sugar > fructose corn syrup, bec.: digestibility/bioavailability differ
4. Eating natural fats also can help with warmth https://twitter.com/rrabagast/status/1361724345018638337