The cake provides the opportunity for the most visual and tactile creativity. The basic idea is to achieve the structure using some sort of frame, then fill the gaps in the frame to give a smooth surface, which is then covered in some assortment of fabric.
The Burning Man Cupcakes, which were built with danger in mind, generally have a stiff wooden frame filled with insulation foam.
The lightweight cupcakes utilize a frame made of flexible irrigation tubing, which has the added benefit of being able to spring back from minor dents. This frame is covered in chicken wire, which is in turn covered in fabric.