If you are taking a lift and going through a backcountry gate, even a small 18L pack should be fine. The stuff that adds volume for me on tours is lots of water, skins, multiple layers for climbing vs descending and food. You might not need any of that except a little food, water and clothes
This year I got a black diamond dawn patrol 32
for spring tours. I went bigger (than 20-25L) because I broke my last 25L pack from overstuffing it with pointy stuff (crampons, ski crampons, axe). That won't be an issue on winter tours.
What I like about the dawn patrol is that the main compartment zipper is against your back, so you can take the pack off and drop it on the snow and access all your stuff without getting snow inside or removing your skis/boards from the pack. The avy gear goes in an outer pocket (pretty normal), there is a fleece google pocket, and big hip pockets for food/phone. There is a 25L version that would be more appropriate for winter use.
The other thing to consider is an airbag pack. These are more expensive ($550++), but are he gold standard in any terrain. There is a handle on the shoulder strap that you yank if caught in an avalanche, and a large bag inflates above the pack to float you to the surface and make you much easier to find.
I have an older BCA float pack
, which uses compressed air to fill the bag. It works fine, but it is a pain to travel with because you need to empty the canister before flying, then get it recharged when you arrive.
Newer/more expensive packs use a battery and fan to inflate the bag. Travel is simpler, and you can more easily practice using them without the pain of a refill. The black diamond jetforce
is a very good one.
An airbag pack makes sense if you expect to go backcountry skiing more in the future. It's overkill for a few days off-piste.
The DaKine packs look good. The pocket for a water bottle on the Mission pro would pull me to that over the heli pro, but I haven't used or felt either. I personally would miss the body-side access on the BD.