My favorite side with BBQ beef brisket is my copycat Costco mac and cheese, although I also really love serving it with twice baked potatoes or creamy potluck potatoes. But you could serve it with baked beans, coleslaw, cornbread, baked potatoes, cold macaroni salad or any other Southern sides you like! I'm also partial to green beans with it, either the plain steamed variety or these amazing green beans with bacon & pine nuts!