In areas where "dead of winter" equals frozen ground and feet (potentially) of snow - best bet is wild game.

With snow on the ground, finding runs to place snares is really easy. Storage of unused meat is a snap (just let it freeze). Tracking is much easier, etc.

Fishing could be problematic if you don't have an efficient method for cutting through sveral inches of ice, though some rivers might not be frozen.

Aside from trees and a few bits of bark and whatnot, there's nothing other than wild game I would think.