[*] Tyre pressure checker/inflater (you can let air out of your tyres for tackling tough snow)
[*] Light snow shovel (just in case you find yourself sliding and end up in a pile of snow, or to help someone stranded)
[*]Old carpets/car mats to slip under tyres for grip
[*]Snow chains
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Anything else?
you could just buy some winter tyres and do it properly