I'm kind of into this one: http://www.brenthaven.com/catalog-expandable-trek-titanium.html
It's expandable, so big enough for everything when needed, but not permanently ginormous to make you look like an ant carrying a nibble of sandwich back to the queen. I'd get the orange, of course.
This is the bag I have. It holds a lot (yet I still always have to carry at least one casebook). People are always like "why are you carrying around so much poo?"
The worst one are the people at my school who carry BOTH a backpack and a laptop bag. Christ get a bigger bag or don't carry so much *&^%. Your cars have trunks. That's my "locker".
A lot of girls at my school have a back pack, and a laptop bag, and a huge purse. It takes up so much room in class.