Forget the dog -- bag is man's best friend. Every day, we carry a bag on our backs or hanging off our shoulders to and from work, school, the gym, the yoga studio, or even a friend's house. Bags have to be big enough to carry the essentials and compact enough that you can squeeze by a crowd of standing passengers on the train or bus ride home; they need to be comfortable to wear for prolonged periods of time, and easy to clean if they get into a scuffle with dirt on the ground or a fresh wad of gum on the seat next to you; and they need to be able to lug around your precious computers and gadgets without the worry that something will break on the way home.