I promise it gets crazy cold if you sit there all day. I didn't hunt in this manner many times, but I did ice-fish for days without a fishing cabin.
1. Layers.
- Sitting there your body won't be generating much heat, so start with thermal underpants/undershirt
- t-shirt and sweatpants, with a warm sweater. I prefer not to wear a hoodie sweater as my parka has a hoodie, and they all bunch up and become uncomfortable
- tall winter boots with non-worn inserts, use regular socks then real wool socks, or sweat wicking socks. It is important not to get wet.
- Full body snowpants are almost enough on their own, as they extend to your chest and back, but leave your arms and shoulders exposed. Get something that is a bit loose fitting as you want heat to build, not transfer out.
- Parka. These can sometimes come in dual layers, with a detachable inner that can be worn for the walk/transition, and add-on parka for sitting still. Get a parka that extends long enough to be able to sit on it.
- Mitts. I like using some nice thin leathers or mechanic type grip gloves, then cover them up with a nice big pair of mittens. I have snowmobile mittens that will keep me warm all day. When its time to shoot, I pull the mitts off and work with the thin gloves.
- Hat. I wear regular orange browning toque, closely fitted and not in the way. Most of the heat is there, but I use the parka's hoodie to take care of the winds and snow. A nice hoodie is key for comfort.
2. bring heat. If you start to shiver, you have to fix that right away. Heat packs can prevent frostbite but are very temporary. If your toes are freezing for example, the only way to get them back to temperature is to either bring them to a 20C environment or to go for a walk. So you want to avoid all that by preventing the effect in the first place. A hot beverage helps, some bring a heatsource. I take blankets and tarps to keep wind and elements from being a factor. I go for a walk to and from the truck every once and a while and get some body heat back. I take my parka off during that walk once I have some body heat worked up. Of course I don't make much noise. Being stealthy takes a lot of energy actually as I work all my twich muscles to avoid making any noise. Get ready to accept that you might need to start your vehicle to get your temperature back. Its a last resource but at that point you've probably exhausted every other option and you cannot continue to comfortable hunt or stay any longer unless you get your heat back. So sitting in the car for 20-30 minutes with a hot beverage should do the trick. If it doesnt and you still feel cold, its time to call it a day and learn from your experience.
In my experience people that get cold is because they didn't prepare very well for a day of hunting. They usually get hot with their jacket and boots during a daily commute so they do not realize the heat lost once you sit still. If you prepare the way I mentionned, you really shouldn't have any issues unless you get a -20 to -30 day with sharp winds.