JC’s information and suggestions are solid. I know this from spending a good amount of years stationed at Northern Tier installations as well as living in the North now.
Some of the items he recommends, such as the 1951 wool US military shirt are worth their weight in gold, so if you can find them in unissued or very good shape, jump on them.
There are a lot of good products out there now, with improved synthetic materials for effective insulation, but if you’re just now beginning to get your kit together, or you’re on a limited budget, you can’t go wrong with the US military surplus items. They work.
Just remember, once you get your equipment/gear, you need to do more than pack it up. You need to train with it.
That means getting ‘out there’ and testing it. Over night. In the cold. And snow. Just sayin’