Having been an elementary teacher for several years I would recommend agains large backpacks that have built-in rollers...they don't fit into most lockers. Also I would get a large 3 ring binder. They also tend to be too large for some desks and they tend to break over time. Basic 3 ring binders are OK if your child is organized. Other than that you might get individual spiral notebooks or 3 subject notebooks.
I hope the school year starts well.