Personally, I use a plain, black, two-straps-over-the-shoulders back pack. (Well, actually mine has all kinds of weird features like a separate internal pocket for your laptop, but anyway...). These days, there's plenty of variation in the world of the backpack. The new "hip" backpacks have only one thick strap, emulating the common usage of just slinging your bag over one shoulder. Likewise, I've seen lots of people using "courier bags" (commonly seen on bike messengers). A surprisingly common feature is having a cel-phone pocket attached to one of the shoulder straps. Of course, I work on a college campus where everybody's hauling books and such around. I also see perhaps more cargo pants than appear in the general population.