They do some Marks and Spencer items and Waitrose.
Wine (check boose is included, can't remember), soft drinks, most sealed biscuits, tinned fruit or jelly for trifles, fruit cake, the extras that you would need for christmas cooking like xmas pud ingredients, maybe dried fruits.
Chocolate mints, ingredients for any special cooking that you might do at Christmas. Frozen deserts. Chocolates.
Pet treats. Batteries.
I suppose it depends on what you have to do over the Christmas season to make it worthwhile, but it's worth a look on the site.
Hope it works out for you, it's a good saving.