I slogged through school with a sturdy backpack - which came with a waist strap.
Ofcourse, I was already used to lugging crap in the Army
If you do stick to plain old backpack, get one which has some kind of backboarding built in - if your bag doesn't keep the books supported, trust me, your back WILL.
And you don't want that happening, no sireebob!
If you're willing to splurge - look for a portable wheelie bag.