I started the year with everything; pencil case, highlighters, pens, pencils, rubbers, sharpeners, different sized rulers, etc, etc.
I finished the year with a pen.
In all seriousness, organisation is really important at A-level. I basically had one large ring binder which I took to college with me everyday. I had four of those A4 dividers and I wrote one of my subjects on each one, so that my large folder was divided into four sections - one for each subject. In those sections I kept all the
current work that I needed so that I had all the work that I would need each day, but not too much.
I then had four smaller ring binders which I kept at home - again, one for each subject. In those I kept all the work we no longer needed in class everyday - like topics we had finished. Then when it came to revision, I had all my notes in one folder.
I also used plastic wallets - not everyone does this, but I found it really useful. I put all my handouts and copied up notes in a plastic wallet before I stored it in my large folder or one of my smaller folders. You can hole punch everything and store it that way, but I had so much work that everything started to rip out of my folder and I started to lose stuff.
I'd suggest buying some cheap A4 notepads. I started the year with WHSmith premium A4 notepads but I went through them so fast, so just settled for the cheaper ones. I had two sets of notes at AS - the notes I did in class, and the notes I made myself as revision.
You could either use four separate notebooks and keep all your notes written up in those. I prefer writing up all my notes and tearing them out of the notebooks so I can store them in my folders in plastic wallets - I just found it easier when it came to revision. You need to be pretty organised to do that though.