Your winter kit should include:

Any personal medications
Fully charged mobile phone with in-car charger
First aid kit
Road atlas (in case of detours and road closures)
Blanket
Shovel
Ice scraper and de-icer
Torch with spare batteries
Snacks (in extremis!)
Extra screenwash
Shop bought de-icing solution is readily available through supermarkets, garages and convenience stores, but should you wish to make yourself a greener remedy, or in case you run out of pre-packaged, you can make a simple de-icing solution using three parts white vinegar to one part water.