I decided to design a barge for the make-it-float challenge. Barges have been used for thousands of years to move things, so why not? My barge has a compartment and two bits for tying off. It is able to support $14 in cargo!
Since I made a barge, I needed a tugboat to push it along...
Note: The barge has been changed from the picture to match the tug. The bits are separate pieces, there is now a deck to match, and the bottom is no longer curved for better printability.
I printed the boat standing strait up on the bow. The rudder and propeller are attached with paper clip wire. Everything else is super glue! except for the deck which fits nicely and removable in case water gets inside.