Okay, I'll forget the usual bits and pieces that I have in my pockets because quite frankly it's alot of stuff and for the purpose of this thread makes things a lot less interesting.
1) Large Fixed Blade:
If you're only having one knife in a fairly cold climate, it better be able to chop easily, so lets say around a 9" blade.
2) Large, Strong, Waterproof Tarp:
Help create a dead airspace to keep you warm at night, stops you getting wet and can be cut into strips to use for securing poles etc... when building a shelter, whilst still leaving enough tarp to use effectively. You can also make a water bag out of part of it if needed, to carry water from a river, stream or other place, and also to store it if you're carful about it (hanging the bag from a branch.
3) Swedish Army Firesteel:
Not as easy to use as matches or a lighter but it'll last alot longer, and keeping the fire going is that difficult part.
4) Very Strong, Thin Cordage:
A variety of uses, including fishing, snaring, neccessary for making certain types of traps and can be used to build shelters.
5) Stainless Steel Vessel:
Stainless steel is long lasting but is not easily damaged by heat, so you can cook with it and it shouldn't develop holes anytime soon, or wear easily.
I've recently been informed that salt and fat are the most difficult foods to aquire in the wilderness, so for an extended stay I might have to put them in place of the stainless steel vessel and the cordage.
Matt