He gathered these after watching his owner pick up some trash. He went and picked up a bottle and gave it to his owner who gave him a treat for doing so. Next thing you know this fellow gathered up all of this in his neighborhood.
@Jeffrey53 some dogs just want to help and when you take them with you when you are doing chores they will try to help. My uncle had a German shepherd who would pick up a small branch and carry it each time my uncle picked up a branch he sawed off of a tree. He had several branches to carry and every time that dog got one he could pick up and dragged it along with him.