Well, today would be one of those dead-of-winter kind of days here in Southern Manitoba. Temps are at -28 C right now and the windchill is the equivalent of -43 C.
If caught outdoors, fire and shelter would obviously be the first priorities ... but a warm tea made from pine needles or rose hips would help keep the chill off and supply you with some vitamins.
Food wise, hunting, snaring or fishing would be the best bet. Red Squirrels, Whiskey-jacks and other small birds are usually plentiful in the Boreal forest, and could be hunted with little more than a few good sized rocks or throwing sticks.
Snares set along rabbit runs are an effective way to hunt 24 hours a day.
Pine nuts can either be gathered direct from the trees or like many times while out hunting, I have come across caches of them left by squirrels.
Winter survival can be tough up here, but it can be done.