You can make gravy ahead of time and freeze it. Jamie Oliver has a good recipe.
You can make stuffing ahead of time and freeze it. Shape uncooked stuffing into walnut-sized balls and open-freeze them on a tray lined with baking parchment. When frozen, transfer the stuffing balls to a freezer bag to save space, and they will keep for 3 months. You can bake the stuffing balls from frozen, just add 10 mins to the cooking time and ensure they are hot all the way through. This chestnut, bacon and cranberry stuffing is perfect for Christmas.
Make bread sauce and cranberry sauce a couple of days ahead and keep in the fridge.
Prepare all veg the day before and keep in the fridge in sealed tubs covered with cold water.
Pigs in blankets can be made the day before. Lay them out on an oven tray, cover with clingfilm and put in the fridge - then they're ready to just pop in the oven.
Make sure everything is defrosted. Give yourself plenty of time for that - better it's defrosted sooner and kept cool in the shed than you're panicking.