Loads...old mats/bit carpet for traction or leaning on if I have to inspect under car, sleeping bag, dynamo torch, rope for towing, sturdy jump leads, screenwash, coolant, compact shovel, gloves/hat/jacket with hi viz/socks, bar of chocolate/water in cabin, scraper, basic toolset etc. All goes in a holdall.
I live 900ft up and usually the biggest problem is others being unprepared and ditching cars by the roadside. I have snowtyres and it sometimes makes no difference how prepared you are or have AA coverage if the road is blocked.