School books made out of the most fragile dragon skin, to give the students the greatest power of all: knowledge.
A quill that writes on its own! When the student thinks of an idea, the quill will write it down on a pice of parchment.
A wand. Each and every one different from another so that it can answer to the right wizard or witch.
Spare house robes ( made from the finest black as black silk) so if they lose one they can put it on and avoid detention

A box of puking pastels  ( made only by Fred and George Weasley )  used when you want to skip class
Lastly, an ink pot filled with invisible ink. You can pass notes around in class and the teacher don’t  know what they say.