Anything you can prepare in advance is going to make your life easier on Christmas day. Two things that will keep just fine are mashed swede and cauliflower cheese. These can both be made the day before, cling filmed, then wacked in the oven, (cauliflower cheese), or the microwave, (swede), when you need them.
Mashed Swede tips.
After topping, tailing and peeling your Swede, cut in to roughly even chunks, then cover in a pan with cold, salted water. Bring to the boil, then simmer until tender.
Drain the Swede, then leave in the pan for a few minutes, allowing excess water to evaporate.
Add a big knob of butter, plenty of pepper, a pinch of salt, and a teaspoon of sugar.
Mash and smash until the consistency makes you happy.