Usually, around the first week in August Target has a good sale. So, then we go and get everything there, and at one time.
As someone mentioned, it seems the lists get linger and more elaborate each year. One way we save with this is teaching our sons to take good care of their belongings. That way things like backpacks, lunchboxes, scientific calculators, 3 ring binders or items for special projects e.t.c can be re-used and/or passed down to younger siblings.