You can do all veg tonight, put them in water to stop them turning colour.
Do you're stuffing tonight also, and could microwave it tomorow to save oven space
You could even do the meat tonight and microwave it tommorow I do prefer meat done on the day though, as do most people I know so you're guests might too, plus it creates all the lovely smells as people walk into your house.
Does your pork shoulder have crackling (the skin) still on? For best pork crackling I would put pork joint in oven on very high, start cooking the crackling then cut it off, put on a roasting tray and back in oven until its done, then put you're pork back in oven with some foil for a couple hours.
When you first do the pork shoulder with crackling, do not assume its cooked.. It won't be, it'll just be done one the outside because the oven was so high, the inside will still be completely raw. so do crackling on 220 and then put pork back in later on about 180 covered in foil