What was Piper doing with the Flannigan's laundry bag in Al Capone Does My Shirts?
When Moose goes outside his family's apartment on the morning of January 9, he finds Piper stuffing extra clothes in the Flanagans' laundry bags. It is the practice on Alcatraz for the residents to put their laundry out in front of their doors, to be picked up by a courier and cleaned by the inmates of the prison. The extra clothes Piper is stuffing in the bags are shirts given to her by her classmates, who have each paid a nickel to have an item of clothing cleaned by "the famous convicts" on Alcatraz.
Piper has collected quite a lot of clothing from her fellow students, and she sneaks the items into the laundry bags of people she knows on the island, a little in each so that she will not arouse suspicion. It is assumed that she is using her own family's bags, as well as those of Annie and Jimmy, who are helping her. She had hoped that Moose would have agreed to put some in his family's bags as well, but since he has refused to get involved, she has to do it herself, in order to have enough space to get all the clothing done. Her plan is to sneak the extra items back out of their respective laundry bags when they are returned, cleaned. She will then distribute the things back to her classmates, in fulfillment of the deal.