Your first priority is to have the appropriate gear to survive in the event your bike is irrepairable. You probably heve the best handle on this being from the area, but it's usually more insulation than you wear while riding. Since it sounds like a remote region, having multiple means to start a fire, and the knowledge of doing so, would be a good idea. The mylar space blanket is another good idea. It weighs nothing and can make a difference if you have to stay put due to injury.
Regarding the bike. Obviously, you need to keep the bike in good condition to minimize failures on the road. Beyond that, the common problems you can realistically deal with are flat tires, broken chain, and minor adjustments. Flat tires require a spare tube (maybe two), tire levers, a patch kit, a pump (CO2 is not very useful in very low temps), a tire boot, and spare tire in case you get a big slice.
A broken chain simply requires a chain tool. In an emergency, you can easily get by with one less link. Carry an SRAM PowerLink and you don't need to worry about nonsensical Shimano replacement pins. Just remove the busted link and use the PowerLink to join the chain.
Forget about spare spokes. Usually the spokes that break are rear drive side. Replacement of one of these requires removing the cassette (or freewheel) to get the old spoke out. Although you could try using a FiberFix emergency spoke, in real cold weather, I wouldn't want to be fooling with it. Simply open up the brake for that wheel if the rim is rubbing, and get to a safe place.
A broken brake cable is dealt with by just not using that brake. This may require you to walk down a steep descent, but that's a minor inconvenience. Replace your brake cables now and it's very unlikely anyway.
A broken derailleur cable can probably be dealt with by using the limit screw to put the derailleur on a middle cog or chainring and use the other derailleur to give your a few gears. You may have to walk up a hill or two, but that's OK. As with brake cables, replace your deraillur cables now and you won't have to worry about it.
You will, of course, carry a multitool to use for minor repairs. If you use a rear rack, a spare attachment screw or two could come in handy as it's not unheard of for them to shear off with use.
If you are using lights to commute, then a spare LED headlight would be good to have. This would double as a flashlight for making repairs in the dark.
Things like freehubs are not worth worrying about. There's little chance of repairing them on the road and they rarely fail anyway.
Finally, if you have a family member at home or with access to a car, you could set up a calling scheme so that if you don't call by a certain time, the person comes looking for you.