An auxiliary bag that attaches to a school backpack (randoseru). It's called a "Sandoseru." I bought it to put in things like a water bottle and gym clothes, and it was very convenient. However, I stopped using the randoseru itself and switched to using a backpack for school, so I haven't used it much. The first photo shows the item for sale. Black x camouflage. A new one seems to cost around 3,000 yen. I haven't used it much, but it was used by a child, so please understand this before purchasing.