Left overs are perfectly safe to eat, either cold as long as they have been properly refridgerated, or hot as long as they are thoroughly reheated. Another way to use the rest of your roast and ensure that it is properly reheated, is to slice it and put it into a casserole dish with gravy, and any left over veggies and put, coverd, in the oven at about 200 C for about 30 mins - it will be properly reheated and not dry becasue of the gravy. Hmmm - always tastes better 2nd day - that goes for most things esp. bolognaise, chilli or soup.