In reply to LastBoyScout:
As with all things mountain, it depends how miserable you want to be. I tour in softshell trousers, a thermal, lightweight waterproof shell and thin gloves. Even when it's been well below zero and in high winds, when touring this is plenty warm enough - it's quite a workout.
In my pack for day touring I have fairly standard winter stuff: avalanche kit, fleece, warm gloves, hat, crampons, axe, skins, helmet, headtorch, nav stuff, food and water. I take risk on not having bulky warm kit or an emergency bivvie. If doing an overnighter, add thermarest (3/4 length - the rucksack works well enough under the feet), down jacket, decent sleeping bag and a jetboil stove. I can cram all this (just) into a 42L sack.
I've gradually cut my kit down and now have what I consider to be a bare minimum. Means the pack is nice and light (good when adding skis to it), and I have enough stuff to survive.