Let them follow the fashion for shoes bags etc in year eight and above. Never mind if it's impractical expensive shite, make it be a birthday present or a something but it's really important when you're a teen.
Plenty of spare biros. Some in bag rather than pencil case.
Emergency money in school bag incase they lose wallet or miss bus or lose bus pass etc.
Instead of spending ages backing books with wrapping paper or rolls of stuff, there are covers that just slip on like a hardback book cover.
A long ruler is important.
Chase them about homework, it's not that there is none they may have rushed through it at lunch instead.
Don't let them take slime or any disruptive toy in.
Be prepared for them to come home speaking in tongues or whatever the local teen slang is. Google is your friend.
Year sevens are exhausted after school just like reception kids. Give hearty snacks after school and let them have at least thirty minutes of zombie out time before you quiz them about their day, homework etc.
Have basic cooking stuff in ready for when they ask last minute for ingredients, and check in bags for letters or the online newsletter as they are bloody oblivious until panic about that thing you know that was due in yesterday.
Food is terrible compared to primary, might need to take a snacks or fruit to bulk it up.
Disclaimer : all schools are different and the above may not apply to yours