Timbuk2 Extra Credit Bag The campus pack that sets the curve. The Extra Credit is a messenger with tuck-away straps that magically transform it into a backpack. Carries like a messenger or a backpack. Hide-away, ergonomic shoulder straps are designed to fit people, not robots. "Hot to Hack" kit includes reflective and customizable, removable Velcro-backed patch logos for optional flair. Lightweight, super durable and waterproof fabric-backed Tarpaulin fabric.