Binder/folder system for high school?

It really just depends on the teacher. Personally, I've learned not to go school supply shopping until after the first day of school. I usually just buy some loose leaf paper and a few notebooks and pencils, then wait and see how each teacher operates. For example, last year my Anatomy teacher had us buy a 3 inch binder and separators for our work. One tab was for class work, one for exams, one for notes, one for homework, and one for bell work. In my math class, however, my teacher had us buy a 3 subject notebook and use each section for something different. Section 1 was bell work, section 2 was class work, and section 3 was homework. It's usually just best to wait and see what your teachers say before buying your supplies. You might end up with a bunch of useless things you didn't need.

On your first day, take a small a4 folder to keep any loose sheets in and ask each teacher at the beginning of the lesson of their preference. This also helps the rest of the class as it may remind the teacher to tell the whole class. Once you know what you need, go and buy it. Make sure to get the right thing otherwise you might spend more money getting the replacement.