Unfortunately i think thats just where those talks have to come in.
I had it in my policies whats expected to be in care like "child sized blankets and pillows" and i had this family that would bring a huge blanket and pillow for both of their children. i knew it was in my policies and written in black and white, i knew the way to fix it was to have a talk, a talk that to me seemed uncomfortable but to the parent was probably not at all, maybe a little inconvenient because they have to get a new pillow and blanket in the next few weeks but yea.
it was just in my head. A fairly simple talk should do it with a list of the only items they can bring and that are expected to bring
OR
you could raise their tuition rates and provide the stuff for them and they could bring nothing at all and you could have exactly the things you need and just that, I've thought about that.