Just bring a notebook, pens and if your doing any sciences or maths, make sure to bring a calculator. The first lessons will always be gcse recap so don't worry about the notes for all the subjects being in one book. After that you should need a folder and refill pads for each subject or I've seen some people using Pukka pads. Use whatever is best for you, though most people will use folders.
One thing I do recommend if you can afford it is an Ipad. You are allowed to use them to take your notes in lesson and it means that you have all your notes in one place and it's all you have to carry besides your pencil case and textbooks. I regret not getting one. 🥲 Really don't stress about it. Unlike me you have more time to prepare. I was an absolute joker and brought nothing except my pencil case and had to borrow paper from people.
Also don't worry about textbooks yet. You'll be told what textbooks you need and will probably be given at least a half-term to get yourself one. This is because students with a bursary still need to gain access to their bursary to buy textbooks.
Depending on what type of sixth form you're going to, you're either not allowed outside at all or allowed outside at lunch. Consider bringing a pack lunch as I'd assume the system to put money in your card may not be ready on your first day or you may not be allowed to go outside yet and you most definitely don't wanna go hungry on your first day.
There is no uniform so dress however you want and relax, You'll get used to it.
I think that is all. If you have any other questions just ask.
(Note: I recommend that you memorise your timetable and get a good insight on the layout of the building and where all the rooms are, you really don't wanna get lost)