I've not backpacked in temps like you might see there in Alaska - but I have done some winter backpacking.

First - winter is going to require a larger pack so that you can fit all the winter gear in it. I carry a ~4500 cu in pack and in winter it is pretty well jam packed - and that's for North Carolina winter. I don't know that you would need a 6000 cu in pack, but you may start approaching it.

For winter in NC - I carry thermals, rain pants and rain jacket, fleece pullovers, fleece beanie and a "buff" - which can be used as a scarf or balaclava. And gloves of course. If I had to extend that for colder temps, I would probably go for some insulated pants and insulated jacket, and maybe another layer on top.

Not sure what kind of tent you have - or if you will be sharing one? That's another thing to consider...

Footwear is another consideration - not sure if you would be hiking on trails or on snow on the trails - so would some type of snowshoe be needed?

Anyway - hope this helps some!