A carton of empty cans in truck box while driving. The cans flew out one at a time hitting our car as we followed behind. One almost hit our windshield. The carton was floating around dangerously. We took a photo as we passed.we counted 8 cans. This was very hazardous and could have been avoided by keeping the empties in the cab of the truck. They must have seen the floating red carton in their rear view mirror.