So, I respect that this is cheesy, and not everyone will agree. But in terms of utility, price, convenience, etc., I find the German Army Knife (from the Swiss Army Knife folks) to be an awesome option. As someone who used to run with a range of Gerbers, Kershaws, and so forth, this is what I've come to use almost exclusively.
I hate tools like the Leatherman, which try to be all things, and end up being shitty at each of them. But to me, this knife really strikes the right balance. I really like having the saw and the knife blade, and use these almost constantly. I've even felled an 8" tree with this (not recommended, but the point is it's doable). The other tools are all non-essential, but having a screwdriver, bottle opener, etc., does come in handy once in a while. And still the weight and pocket profile of the knife is totally reasonable. The one-handed opener works fine -- it's not as fully smooth as a good single-blade knife, but it gets the blade into action quickly enough for any practical purpose (it's not like I'm using it as a switchblade!).
I have used the knife extensively in cool, wet, and sandy environments, and a bit in the snow, but not so much in extreme cold. So I can't attest to its performance there. But this is essentially the same model as used by military forces where it is very cold and there's lots of snow, so my guess is it will hold up well.
There are several "flavors" of this knife around, but here's a link to one for reference:
http://www.amazon.com/Victorinox-One-Hand-Trekker-German-Multi-Tool/dp/B001B197RE