When you first see ThinkGeek's Captain America backpack, we suspect two questions cross your mind; "How will my friends cope with owning substantially-inferior bags?" and "How far can I throw that thing?" We can relate with the latter, truly, but please don't try to stop evil by throwing your stuff. A pop quiz just isn't grounds for frisbee-shielding your professor.
Heroic ventures aside, you can still justify keeping Captain America's shield close by using it to carry your daily vitals. This passive version uses firm plastic for its 18" diameter shield as well as polyester for its straps and backing. For a general sense of capacity, the internal laptop pocket can manage a 15" Macbook Pro.
Just promise this won't lead to a drift from your dream team, okay?