This guy made a functional boat out of plastic bottles. The only question is - did he drink their contents first?
Here's an interesting idea- screw the tops of assorted plastic bottles onto a sheet of plywood, and then attach the missing bottles.
Now repeat, and then set sail with said 'water craft' at the nearest boat launch.
Well, it floats.
It doesn't look too comfortable though and I wouldn't take it too far from the shore. If this were the brainchild of some school kids then we might be laughing and saying "why didn't we think of that?"
At least they recycled and reused!