Backpack of dimension

A backpack with two side pockets. The big center pocket is a pocked dimension 25x25 ft square. People can enter and leave the dimension at will, the backpack opening stretches to allow access. The owner of the backpack can decide what the pocket dimension looks and feels like. The two side pockets are bags of holding. Bags of holding can be put inside the pocket dimension. Physical items like a bed or chest have to be brought into the dimension.