dirt piles, later turning to snow piles (similar to leaf piles)
kick it up to reveal some random ground-drop loot table stuff, maybe berries and nuts and the possibility of a small animal that was burrowing there.
Maplesap should flow more during winter, and we should be able to boil it in a cauldron and make maple syrup, which is a versatile candy/dessert making ingredient, or maybe even a dessert-only condiment?
Also, the Canadian treat - maple syrup on snow.
Animals like Ptarmigans, Reindeer, Golden Eagle, Eagle Owl should spawn in more biomes during winter, as though they are travelling more to forage for food when it is scarce.
Weird low frequency noises from frozen bodies of water, can maybe trigger lore events.
winter mushrooms like oysters, turkey tail, enokitake
rare, high tier winter curio?
Snow Roller
Frost Flower (ground frost phenomenon)
Frost Flower (sea ice phenomenon)
Hair Ice
winter moth, arctic fox, snow leopard, caribou, angry hungry winter bears
edit - I don't think this is a grab bag, just a way to collect a bunch of winter-specific content ideas, hopefully other people can add their own too
Another idea -
Logs in a swamp over winter should turn to mirkwood logs, and mirkwood logs in a swamp over winter should simply disappear, like the ice and thaw decay the wood 1 stage. Could be an easy and semi-realistic way to deal with excess logs?