Do you really need to take all the textbooks with you everyday? In most of my classes I don't need the textbook for lecture time. It stayed home for homework.

Can you take part of the text book at a time? If you are not planning on selling the books back, how about some home surgery on those books? I have a Calculus text book that is used in my college for 3 classes: Calc I, Calc II and Calc III. I cut mine apart, into 3 sections, at the chapters that are used for each class. I used some mylar for new covers and some packing tape to cover the glued binding, and just took a thin part of the textbook to class each day. Other students asked me where I got the thin textbook!

Also, for binders I use the 1 inch ring ones with thin flexible heavy plastic covers, instead of the big ones with the thick covers. Takes up less space in my pack. I can add and delete notes as time goes by and keep my commuting load light. I use a separate binder for each class. Some of them are left home on some days.