An auxiliary bag that attaches to a randoseru (Japanese school backpack). It's called a "Sandoseru." It can hold things like water bottles, gym clothes, and lunch uniforms. It was very convenient, but we switched to using a backpack for school soon after, so we didn't use it much. The first photo shows the item for sale. Black x camouflage. New ones seem to cost around 3000 yen. It hasn't been used much, but it was used by a child, so please understand this before purchasing.