cold weather camping and hiking (and climbing) beta (that i learned the hard way)..
-when your mittens or gloves get wet (they will) take them off and put them in your jacket, as close to your skin as you can bear. they'll dry out while you soak the new pair.
-zipper pulls. make huge ones out of thin accessory cord so that you can zip your layers open and shut in high wind, with ski goggles on, wearing huge overmitts. just try that with a normal zipper tab or even the factory-installed mini-pulls that come on brand name gear. if you have a couple pockets that open from the same vicinity, use different color cord. my pulls for bitter weather are about 6" long, but you cant overdo it, really.
-you cant have too many hats. a neck gaitor is a marvelous thing. head layers go a lot further for the weight than everything else. carry lots of spare hand insulation. gloves are much colder than mittens, but you knew that, right?
-need calories? my favorite active snacks- snickers (freeze but they break easily and taste great. 510 calories in the king size), raw cookie dough (buy a roll and chop it into a couple pieces and find a way to store it. about 2000 calories for the whole roll), cheese (string cheese freezes, but it warms quickly in your mouth and then tastes like.. string cheese.). if you need lots of snacks, but dont want to bother with unwrapping snicker bars in 40 mph winds with mittens on, just put all your snacks in the freezer the night before, then the morning of unwrap everthing and put it in an outside pocket. the frozen food (cookie dough might not work..) will stay frozen and won't dribble and mix and you dont have to unwrap things or find somewhere to put the trash.
-hydration. people always tell you you need to hydate. you've heard the buzz right? well, theres few times more important to be topped up than in serious cold weather. but cold water sucks. before a climb i get piping hot water and mix in whatever drink mix i have around (gatorade, juice concentrate, lemonade powder, whatever), plus a pinch of salt. yes, its not the absolute ideal hydration elixir, but thats not the point. you need the water. put whatever in it you need to make it taste good to you. the most important thing is that you are drinking enough, not that the water that you are drinking are incorporated into the body as fast as possible. besides tasting better, the drink mix will also make the water slightly harder to freeze.
remember to wrap your water bottles with the spare layers in your bag, and consider having a bottle very accesible, like in an inside pocket of your shell. the hydration bladders are nice but i have never seen a system that wont freeze in extreme temperatures (though it may exist). i have a sling which goes around my neck and under my arm that holds a 1L platypus bladder. i keep a pop-top on it so i dont need to use my hands to open it, and it keeps from freezing inside my shell.
if you keep heated water in your pack, dont put it near your goggles. it will fog them.
-when water bottles, trekking poles, etc freeze shut/open, breathe on them repeatedly, or put them in your jacket to thaw them.
-trekking poles with the twist locks are superior for bitter weather. you can open and close them with enormous mittens on, unlike the BD flicklock poles for instance. if you are hiking in snow, or some other catchy material, they can eventually work loose from the continual twisting motion. to remedy this before it takes you by surprise, either tighten it by hand periodically, or while hiking: jam it into the ground and twist the handle in the tightening direction forcefully. use snow baskets. not only do they stop you punching into snow, they also stop the tip of the pole from constantly being caught between roots and in rock talus.
-to use cameras in the cold, keeping them warm is a nice touch. film cameras, in very cold dry conditions, may have tiny static discharges during winding which leave marks on the film. digital cameras suffer from battery drain, which means you either need to keep the camera warm, or have a lot of spare batteries, or use expensive batteries that are not as affected by cold. when you come in from the cold, put the camera in a ziplock bag to warm up, otherwise ambient moisture condenses on and inside it.
-tie your shoelaces so that you can get them undone with cold hands. a double knot won't work here, and a bow comes undone too easily. my favorite is a bow with a double wrap. ie: when tying the bow, hold one loop in one hand, and wrap the other lace around it twice (not once) before pulling a loop through. it takes a little more finagling to cinch it tight, but it never comes undone and pulls out just like a bow.
-more socks does not mean warmer feet. if your boots are sized for one fat pair of smartwool, and you decide to cram in a second sock layer for extra warmth, you literally shoot yourself in the foot. it squeezes the feet, reduces circulation, and makes it that much harder to keep them warm.
if your shoes/boots are not warm enough, you need to get bigger boots to fit more socks, or more specialized cold weather boots. or you can dabble with vapor barriers and neoprene socks, which have their ups and downs.
-ski goggles are wonderful for keeping blowing snow and wind out of your eyes, but they were not designed for hiking: heavy exercise with low speed. because of this, they fog very easily and once fogged will stay fogged. store your goggles in your pack, not in your jacket, because warmth can fog them. dont use them unless you need them. when you decide you need them, put them on and if possible refrain from using them with a balaclava/ski mask which diverts a lot of hot wet breath upwards and makes them fog faster. when you take them off, keep them cold (dont move them up to your forehead, or down around your neck when not in use) and dont let snow get in them. if you get snow and ice in them, shake it out before putting them back on so it doesnt melt in.
to reduce fogging, consider taking out the foam pieces on the top and bottom of most goggles that stops snow from blowing in. it makes the goggle colder, but dramatically increases airflow. also consider smearing some antifog on the goggles before heading outside. every single goggle manufacturer swears it will destroy their factory coating and do bad things, but i havent seen anything bad come of it, and a layer of Cat Crap (tm) or similar seems to make it easier to keep defogged. in addition, when they do fog, i can take them off and let the fog freeze, and scratch it off with a fingernail easier with the coating.