Backpack for me. I used to carry around my binder outside of my backpack, but when I got a backpack that had 2 large storage areas, I moved all of my folders into the one storage area, and my binder now rests in the other... I use it as a back support, plus it keeps my folder of drawings and extra paper from getting messed up. Other than that though, I never even touch it. It doesn't even have anything in it, really...
Also, I need a backpack, because I always bring my CD player and (BIG) headphones to school with me, and they have to be out of sight when I'm in the hallways. So, I can't carry them around with me. Plus I have little things, like spare leads, erasers, and pencils with me... and a piece of sandpaper, lol... All of that goes into my smallest pocket, which is still big enough to just fit a normal size schoolbook. I keep another CD player with me, as well as a small case of CDs... but those go into side pockets on my backpack. Oh, and I have a flap on the back where I keep my everyday pencil, fancy ballpoint, and 4-color pen... I also keep my calculator in there (since it has 3 pencil/pen size slots, and a big calculator sized one) and I keep my straightedge (basically a ruler with no markings) behind my calculator... If I can find a relatively thin pencilbox, I would also bring my felt-tip inking-quality pen and crummy Crayola colored pencils.
In the big pocket where I stuff everything, I have my Geometry book (very thick), and all of my folders, which are overstuffed from all the papers I get at school. I also have 2 note books, one of which is completely filled with Geometry notes, the other I had to start since my first one was full.
Lots of stuff, and when I get library books, it can be a total PITB (Pain In The Butt) to haul around...
Oh, and there's my coat, but I wear that between classes... Sometimes, I'll hang it over my arm. Try carrying all that without a backpack!!
I would use my locker, but its totally out of the way from all of my classes, and I don't have a lock for it anyway. Besides, I hate lockers.