This happens during the dance workshop at the end, when Cooper, Charlie, and Jody are all performing Cooper's ballet. When Jody comes out on stage by herself, in the blue dress, she has a straw bag over her shoulder. Then Charlie takes the bag off her shoulder, and in the next shot, you can see that he set it on the floor next to her. They cut to a shot their upper bodies, and when they go back to the full shot, the bag is gone, and it never comes back.