Where I live, every summer, we have what they call the milk carton derby. All kinds of "boats" are made from various types and kinds of containers. mostly for milk, the most common being the typical 1 gallon plastic jug held together with the handyman's secret weapon, duct tape. I even saw a refrigerator box once which was simply covered with plastic garbage bags taped to keep the cardboard of the box dry. I'm sure you can come up with something, if you are really serious...