You could parboil your potatoes the day before. To roast, put a big dollop of goose fat into the pan and use your hands to get them all coated.
Whack into a hot oven
Parsnips just need maybe some honey and oil. Don't need parboiling.
You could do a carrot and swede mash with butter, pepper and nutmeg the day before. Zap it in a microwave when ready.
Also, maybe do red cabbage braised with apples, raisin and bacon the day before and heat up.
All sorted apart rom maybe one green vegetable which just needs a quick steam/boil.