In our rather insane competition called Making It Move the next contestants hail from San Diego and Lanzhou and enter the arena with a potato here. Their contraption can obtain a speed of around 3 body lengths per seconds with a lifetime of up to 2 minutes.
The potato is sliced into 2 mm thick pieces and then punctured to a 1 mm diameter torpedo. One side is coated with epoxy resin. The medium is a solution of hydrogen peroxide. Autonomous movement is created by the oxidation of hydrogen peroxide by catalase present in abundance in the potato. The generated oxygen bubbles provide the thrust. Potato out-competes carrot.
Without any irony the contestants argue their invention is really cheap: "Since a single potato motor corresponds to a tissue weight of ca. 1.5 mg, over 500 000 motors can be prepared for only $1".

Movies here