When I do a Sunday roast I do like adding some roasted vegetables on the side. One time I did this I did butternut squash and heritage carrots. This was seasoned with salt, pepper and fresh herbs.
Another thing I do with roasting vegetables is put them at he bottom of the roasting pan. Here for roast belly of pork I have pepper, butternut squash, onions, mushrooms, fresh herbs and as it was pork, some apple.
This helps keep the roast moist and tender, whilst also adding flavour. When you leave the meat to rest, you can finish the vegetables off in the oven, or use it as the base for some gravy.