This is what works best for me in Montana: I tried the Sitka and love it when moving, but prefer my KOM and Gray Wolf (GW) wool when sitting on stand in cold weather. I wear wool long johns, wool shirts (Filson or Pendleton), and a fleece or wool vest underneath my KOM or GW pants/overalls and coat. Like Mike mentioned, keeping the head warm is paramount to keeping the body warm, I wear a thin balaclava over my head and under my wool with wind blocker KOM or GW Bomber style hats. One other thing I learned from Doug Campbell that helps a lot in windy conditions is to use of a silk neck scarf wrapped around my neck to help regulate the heat; Guess there really is a reason all the cowboys have been wearing them since before I was born (I am a slow learner at times). If it is warmer than zero (F) I cover my face with half a spandoflage head net (I cut the top off and wear it upside down) that covers my nose, face and ears, instead of the balaclava, this allows the moisture to leave and not build up too much, while staying tight to my face. Most thrift store or army/navy wool works great if you can control the bulk and have some type of wind blocker to go with it, but I have never regretted buying my KOM or GW wool.
What is on my feet depends on the temperature; Down to 32 irrigation boots with wool socks, from 32-0 Schnees boots that are a size too large, which allows for an extra pair of socks as needed, 0 and below a set of Mickey Mouse boots that I put on when nearing or while in the stand (don’t walk very far in them or your feet will get sweaty and they will be cold for the entire time on stand.). One other thing that helps keep my feet warm is putting on a set of “bear’s feet” made for stalking critters from the ground. These go over your boots, have a lot of fluffy stuff like fleece, and about half an inch of foam on the bottom, which insulates your feet from your cold metal tree stand. With these on, I have found the Mickey Mouse boots are not needed until it gets to -20, at which time I start questioning my sanity but remain on stand anyway.
Like others, the use of hand warmers can really help, if used properly. I don’t put them in my boots because they make my feet sweat, and then stop working due to lack of fresh air after an hour, then my feet gets extremely cold. However, I do sometimes put them over my toes, outside my boots, and underneath the “bear’s feet” which keeps the air flowing to them and do not over heat the feet. If it is less than 20 degrees I keep a hand warmer in each of my jacket pockets for the entire hunt and sometimes put one over my right shoulder to keep it warm and flexible (had shoulder surgery). Last year they came out with warmers for the lower back that are in an elastic band and they work well at maintaining body heat, if kept outside of your shirts and beneath your jacket.