I have been using my Maxpedition Falcon II at college for the past 2 years and it is holding up spectacularly! It is slim and fits two books and a 1.5" 3-ring binder very well. It has a nice pocket for pens and a perfect pocket a for a TI-83 sized calculator. I attached a 10x5 water bottle holder to the side and it works very well to carry a Guyot around. When out and about in the woods, you can also cram a GSI bottle cup and Maxpedition Tactical Can Case in the bottle holder for a nice little kit. If you are not bringing a tent or sleeping gear, the Falcon II would provide you with plenty enough space for a day's gear.
Simplicity is the ultimate sophistication.