2 pencil cases in his bag, one for the every day stuff pens, pencils (they usually have to have a pencil sharpener even if they have a mechanical pencil) glue stick, rubber, school sanctioned calculator, highlighter and so on.
The other pencil case had compass, protractor, colouring pencils and SPARES of the essential equipment. So spare whiteboard marker, spare pencil, rubbers etc. Don't underestimate how devious other children are at nicking stuff so you get in trouble for not having essential items.
Also, agree with Teen at home have the same stuff so that your child never takes that school pencil case out of their bag, because they may leave the whole thing on their desk. (been there done that, I spotted it and jumped in my car to catch him on his walk to school)
Buy a pack of 12 glue sticks. Schools tend to operate on a print out system so lots of things to stick in books rather than using text books.
Spare £1 for anything he may need from student services, and attach the door key onto some elastic and attach it to his bag. That way he won't lose it, just unzip a pocket, stretch up the key, unlock the door, remove key then put it back into bag and then open the door. That way the alarm isn't beeping whilst they try to wrangle the key out of the lock. Once inside, shut and lock the door, then put in the alarm code. Safety first.