I always start thinking about Christmas in the summer holidays 
In January I picked up some new baubles & crackers (pulling kind) which I'm really glad about. I prefer having a real tree but do have a decent-ish fake one in the attic.
Got 6 nut roast mixes, a bag of frozen roast potatoes (potatoes were hard to get for a while round here) various tinned & frozen veg & instant gravy so Christmas dinner is sorted even if it's not perfect.
I've picked up a few stocking fillers (agree with PP who said supermarkets were filing empty spaces with left over Xmas stock). Things like small lego sets, make your own dragon egg, pocket kite.
I have lots of wrapping paper which will be good to use up, same with cards.
I've been picking up puddings for winter like custard, rice pudding, cake mixes etc. Also dumpling mixes, red lentils, curry sauce etc for good filling food. Also long life squirty cream, vegan marshmallows & hot chocolate.
I already have waterproof trousers, boots, gloves etc so we can get the DC out & about. Simple pleasures like looking at christmas lights may be more important this year.
Will be watching this thread & the Christmas threads for ideas!