Hi Nick
Food – yeah, can be a problem. Sometimes if we are *very* tired in the evening it can be difficult eating. The stomach is just too tensed up. The same problem affects climbers in the Himalayas – they are too stressed to bother eating in the evening, so they go to bed without much food, and can't sleep because they are too cold, etc etc. And by not eating they don't drink enough, which causes more problems… Vicious circle.
So we start by having some '2-minute noodle soup'. This gives us warmth, liquid, electrolytes and stimulates the appetite. Seriously. Well, it works for us anyhow.
Hydration – I know. We seem to drink a fraction of the amount of water other people drink. It may be a matter of experience or training. Not sure. In the snow or very cold weather the air is fairly dry so you can lose more water by breathing. We don't worry about it, but we do keep a water bottle in the tent at night, and if we wake up thirsty we do drink – just a sip at a time. A sort of slow rehydration maybe. If we are short on water, at a high dry camp for instance, we still drink. Better to have the water inside me than inside a bottle.
Hood on quilt. Well, ever pulled the bedclothes over your head in bed at home? You breathe out sideways. The same applies when I have my head on my little pillow and the SB hood over my head. I leave an air gap in front of my face, and that seems to be quite enough. Having warm ears and a warm head sure is worth the effort of maintaining the air gap. If my head is getting cold through lack of cover, it takes less than 1 minute after I flick the hood over my head for me to really notice the improvement in warmth over all.
Feet. I usually arrange any spare clothing (not a lot of that!) folded up at the foot of my 3/4 length air mat to help keep my feet off the ground. Without some padding there I find that whatever bit of me is resting on the ground does get cold. The down under my foot gets squashed of course. That's why I am never very impressed by the idea of extra 'foot flaps' in a SB: it's not the down on the top of the bag which is failing to insulate.
Sit Mats. Shameful things, they add to the load. Funny thing though: we (and many others) think they are worth it. I am talking about a bit of CCF maybe 15" x 10" x 1/2". Great for sitting on when the ground and everything else is soaking wet. Also great on snow. Also good for sitting on when cooking dinner, and for tucking under my feet when I go to sleep.
We first met these in the UK, many years ago. Meal breaks were uncomfortable as we always got cold wet backsides. Wet logs, wet rocks … So part-way through the trip I bought two commercial CCF sit-mats. Maybe the big surprise was that the gear shop in the little town had them in stock. Anyhow, at the next meal stop when we sat on these, we simultaneously turned to each other after maybe 30 seconds and each said "I've got a warm bum!". We have carried them ever since.
Cheers