OK you have uniform list.
If they have school stockists, don't assume everything has to come from there. Our school at one point said school skirts had to, but hardly anyone did and that requirement has now gone, I think.
Buy big: e.g. blazers with arms down to little fingers. Lots of people do this and it increases how long they last. (Or have a small child, DD1's blazer lasted 5 years).
Don't buy too soon because of growth spurts.
If you are struggling, some schools have quiet second hand uniform for children in need. e.g leavers are asked to donate uniform back so it can be redistributed.
Rucksack / school bag.
You may be asked for contribution towards art sketchbook / pencils, & food tech. At our school you just provide the food tech ingredients yourself when they are rotated onto that (only about 8 weeks of the year).
Pencil case containing pen, pencils, selotape, pritt, geometry kit, calculator. Don't buy a calculator without checking the recommended model and whether the school provides it at a discount.
Many schools round us seem to do a France trip at the end of year 7, but they have a maximum number so not even half the year group go. but if you wanted something like this you might need deposit money to hand.
I have found it useful to have at home
- a French reference book (verbs & vocab)
- a CGP KS3 Science guide
- a second pencil case so the school one stay in the rucksack and doesn't get forgotten
A big potential hidden expense is that some school assume pupils have access to a laptop and printer at home. They should make allowances/arrangements for those that don't, but I guess some will be better than others. Some schools set homework electronically. (Ours doesn't).
Secondaries seem to have far fewer random requests for money than primary schools, but there still might be occasional charity days.
Transport costs?
School dinners costs?