For years, my go to saving grace for long days in the treestand were those little air activated handwarmers. The larger ones last 18 hours and besides having one in each pocket, putting a couple on your lower back can be very helpful. They are realitvely cheap and are easy to find. In the past I have also used the lighter fluid and charcoal type handwarmers. Again besides your hands, they work well for warming other parts of the body. I have also used a sleeping bag when in a treestand, but nowadays they make those body bags made specifically for hunting and are easier to get in and out of. For long days in a blind, one cannot beat a small LP heater. They also now make small compact battery type heaters, but battery life would be my concern. Keeping warm as I get older has meant shorter sits, and stands close with easier access so a heater can be used, or I can come and go more easily. It's not the same as packing a treestand in 3/4 of a mile and hen freezing for hours waiting for a buck, but at least I'm still getting out there. Sucks getting old, but it beats the alternative.