Year round I try to do a 5 km walk every day. In winter, that's normally with snowshoes. Every couple of weeks, I do 10 km, even with snowshoes.
I usually get in few hours of ice fishing a couple of times a week. My fishing holes are 1-5 km away, and I snowshoe out and back, hauling everything on a sled, so that few hours of fishing sometimes uses up all the daylight hours.
I try to get out at least once each winter for a night out in the tent. Usually within a kilometre or so of home, but occasionally as far as 5 km. This winter, I might take advantage of my new status as a retiree to make that 2 nights and maybe push that distance to 10 km.
When the shop is warm enough, I work on whatever my current project is.
When the shop is too cold or I don't have a project calling my name, I try to get in some time on learning a new programming language, programming something, or online courses in everything from philosophy to physics and beyond.
Or just read. I go through about 150 books a year, pretty evenly mixed between science fiction, mysteries, and seemingly random nonfiction.
This will be my first winter as a retiree, so it'll be interesting to see if there are any changes or new stuff.