This i't day pack,but it seems input on clothing is useful.The GI wool pants are a great piece.I use the German ones.I fitted the Carhart rivet type suspender buttons to them and added Carhart suspenders.
In a slightly different direction,two forces that will beat you down are wet and wind.An outer shell garment,like a parka with pants or bibs of a breathable Gore-tex like fabric are very good.Most of them are horribly noisy.
Cabelas and Browning and a few other outfits offer a quiet finished hunting breathable shell garments.I like Cabelas rainsuede.It is considered packable.It will stuff in its own pocket.I suggest uninsulated.
For undergarments,study the REI catalogue,and Cabela's REI will educate you .Look at 'Base Layers" Underarmour makes some good stuff.Merino wool sox work for me.
The synthetic underwears can be layered.THen,if needed,a layer of fleece is good.Polartec,etc.It is light,warm,and dries fast.
Then,I like a GI field jacket liner,the thinsulate one,as an aditional layer over the pile.You may want to have a synthetic fill(rather than down) vest with some loft to the fill,but a thin,light shell.
Have with you the knit wool gloves with no fingers,like Belker wore on "Hill Street Blues" Get the ones with the rubber polka dots on the palm.
These aren't enough for real cold but they camo your hands and are often enough.For cold,I use GI Artic mitten shells with the trigger finger over the fingerless gloves.
Those teabag type chemical handwarmers are good sometimes .Ice fishing,I put one in each glove.
If you are using a down bag,here is a tip.They have steamy air in them when you are nice and warm.When you get up,it freezes to ice crystals in the down.So,as soon as you get up,while the bag is warm,have a mesh stuff sack andstuff it to drive the damp air out.,then pull it back out,fluff it a bit,and lay it on your cot.If you get some sun,sun your bag.
Have a great trip!!