Lots of excellent ideas thus far. I've thought about those heater body suits, but I am on the fence about feeling comfy up in a treestand with my arms zipped inside and the safety aspect (yes, also using a safety strap). I always carry my top layers, both top & bottom, to the stand location adding them after the walk, which always keeps me warm. I've noticed that my worst areas are my feet & hands and use heater pads on both to help. I never wear the same hat as the one I walked in wearing, putting on a dry and scent-free one I carry inside my pack. Recently the use of a neck gaitor also added at the stand location has proved to help as well. I have also used an insulated muff with hand warmers inside as a great way to keep my hands warm, it's warmer and more convenient than using jacket pockets for me.

Something else I've found that works really well for me is the use of boot blankets, insulated "booties" that simply slide on over your boots. If your feet are setting on a metal platform, the temperature they are exposed to is much lower in very cold weather than what they would be exposed to on the ground. The boot blankets ensure that the bottom of your boots are not exposed to those very low temps ( a piece of carpet can help there too). These work way better than toe warmers for me in really cold weather because there's less chance of overheating your feet getting to your stand if there are no toe warmers in for the walk. I'd be interested in trying the newer heated innersoles by thermacell, but no so interested in their cost.