The locks must be purchased from school, they cost about three dollar each. Each lock comes with a combination, make sure you know what the combinations are in case your child forgets them. Don't stock up on too many other supplies before the first day of school. Different teachers will ask your child to bring in different things. Some like erasable pens, some like regular pens, some want blue ink some prefer black.
Some teachers only allow pencils and others prefer mechanical pencils.
Wait until your child brings home the supply list from the teacher before you buy all the wrong things. If your child is taking a bus expect a big mess the first few weeks. Don't be surprised if bus stops are changed or moved, or bus numbers or routes are changed. They may get home later than usual the first week or so. Eventually it all works out.