Mostly already been said, but a couple of things that I’d add:
– NeoAirs are great, but in those temperatures you start to notice the fact that (unlike all other Thermarests) they have no foam / insulation, other than the air you’re putting in. I’m not long back from the Himalaya where I used one with a good (closed cell) sleeping mat and was warm and comfy at a lowest temp of -17 deg C. I put the warmth down to the sleeping mat and the comfort down to the NeoAir.
– The advice about star jumps before bed is not to be underestimated, if you get into your bag cold, all it’ll do is keep you cold.
– give your bag a really good shake out before getting in (help ‘loft’ it). If you can, then get it out in the sun to air / dry off at some point (while you make B’fast or in the afternoon, when pitching tent).
– Keep a pair of clean, dry socks for sticking on in your bag, take the ones off that you’ve been wearing and have them in your bag to dry out. Give your feet a really good rub / warm up before putting them on (maybe even talc up – try Gold Bond blue talc if you’re in the states).
– Loads of hot food / drink (if you’re worried about having to piss in the night, then carry a spare Nalgene….. just don’t let it freeze, as trying to melt / hack frozen piss from one the next morning is fairly emotional).
Any chance you could stick some photos of your trip up once your back? I quite fancy heading out that way sometime.
Cheers.