I would buy the Casio fx 83/85 calculator, the one you can get I most supermarkets, they come in black, blue, Pi and for the first time this year white. It is well made and will last until the end of gcses in terms of it's functions. Most supermarkets include it in their back to school offers when they do those.
But a cheap geometry set, but keep it at home. A long ruler is not necessary for most of the time, either buy a 15cm one if your kid has a small pencil case, or a folding one, long ones get post as they don't fit in pencil cases.
Identify everything, but doesn't need to be as e,harassing as a name on things like pens and pencils, a blob of nail varnish will do!
Have plenty of spares at home, e.g. Pens, pencils, but just a couple at a time to take to school!