For me, nothing because I keep my bag packed for winter even in Summer. I figure it’s easier having there in the bag all year long vs remember to put something back in later and if it’s summer and an item I don’t need I can always shed it.
While not really related to my bag, I do always make sure I have a field coat, hat and gloves with me when I get in the truck to go anywhere.
I also have an “extra clothes” bag in my truck that has a pair of jeans, hiking shoes, wool socks, shirt, underwear, t-shirt, sweat shirt that I keep in the back of the truck year round (keeps me from having to go on a hike in the woods in a button down, dress slacks and oxfords, lol).
Items I carry that are for cold weather: wool blanket, balaclava, big packet of hot hands.
One thing I do with my pack is keep an inventory spreadsheet of all the items in my pack. I denote items that have expiration dates and make sure I change out any items that are about to expire twice a year (June and Dec). Typically in June I pull all the items from the pack to make sure everything is holding up and nothing needs replacing.