We just got back from my parents in WV where the snow was pretty mild for them, usually they get accumulation measured in feet not inches.
I always take our camelbaks and have large water bottles in the cooler to fill them with and each of those have our base layers kept in them as well and the wool socks and some gloves. Then all our winter coats are packed, sleds, my ALICE pack full of additional gear, fleece blankets for all, etc.
I probably carry enough weight in gear to keep me from ever sliding off the road.