Do you want leftovers? I like to send guests home with some so they can have a lazy day. But if you don't need leftovers 4 adults don't need a huge amount of food. The biggest issue with Christmas dinner is the size of the joints which means long careful cooking and limited space for sides.
Plan all the meals around Christmas.
Start buying extra ingredients now, dry stuff to begin with, or things that can be frozen. Eat your way through your current freezer stash to make space.
Buy cards and stamps and do a few each night.
Sort out gifts to be sent abroad as posting dates are early.
Sort out children's gifts
Book appointments for hair, nails, tan etc if you need
Wash and iron bed linen, table cloths, napkins over the next few weeks
Check that you have enough oven/serving dishes etc
Lists lists lists are your friend
A few candles (leds with small dc) and some Christmassy music and you're half way there.