Prepare campfire or grill for low heat. Arrange bread slices on a greased double thickness of heavy-duty foil (about 24×18 in.). Bring foil up the sides, leaving the top open. Whisk eggs, milk, syrup and vanilla. Pour over bread; sprinkle with nuts and 1 cup blueberries. Fold edges over top, crimping to seal.
Place on a grill grate over campfire or grill until egg is cooked through, 30-40 minutes. Remove from heat; let stand 10 minutes. Sprinkle with remaining blueberries; serve with additional maple syrup if desired.