Lee,
If I am doing a big BBQ I always smoke the day before, wrap and then reheat before serving. You may want to add some stock or bouillon to it before reheating. I have found that waiting a day before reheating and slicing tends to intensify the flavor. Last week for the 4th I did 2 12 lb. briskets and a 13 lb. pork butt/shoulder on the 3rd and served it on the 4th. As usual we ran out of meat.
As far as left over brisket, we saute some finely chopped onion in chopped bacon, *** the meat and some medium to dark beer and let it simmer for and hour or two. Makes great sandwiches.