I don't normally drink spirits but I like to make sure that I have some whisky over Christmas and the New Year (even though I might not actually drink it!). Similarly, it's the only time of year that I'd normally consider buying any form of 'bubbly' (whether it's good quality Champagne or cheap Cava/Prosecco).
While I get through quite a lot of chocolate bars (e.g. Mars, Snickers, etc) during the year, Christmas is usually the only time that I buy Roses (or, far better, some nice Belgian choccies).
Some things I like (such as booze-soaked Stollen are only available at Christmas - although it probably won't be long before the supermarkets start stocking it all year round!
I also find myself being tempted by things like duck breasts, venison steaks and expensive fish, that I'd not normally buy during the year.
I've got some smoked salmon in the freezer (that wouldn't normally feature on my shopping list) - but that's for the cats!