I'm a third year year industrial design/mech eng student studying in Australia (fun :-) ), and for a recent assignment, we familiarised ourselves with the movement known as redesign - a collaboration of product designers who endeavor to take used components/materials, and make new products from them in a sustainable way (http://www.redesigndesign.org/ is a main website if you're interested).
My personal project, therefore, was to prevent the purchase of plastic P.E.T water bottles by devising a cup that was convenient and portable to carry around and use every day (after all, in many places, the health standards are higher for tapwater than bottled). Moreover, it had to be long lasting, easy to clean, recyclable, and able to hold the hot uni-cafe coffee I inevitably need, after staying awake all night working on things like, well, this.
The result is a cup that can hold more than a can of soft-drink when full, yet is about 2cm thick when flattened, and fits easily in a pocket (it can also be looped securely onto a belt). The shape does not transmit heat to the hand easily, and best of all; it's made mostly from the polypropylene covers of used folders where the spine had broken. I write this instructable in the hopes that others may also manufacture one, and I intend, with time, to refine this project further.