I was in a similarly poorly specified contest in the 6th grade. The goal was to take a single large sheet of construction paper and build a paper airplane. The only metric was distance covered and weighting your plane was allowed.
Day of the competition everyone else in class has their planes out, while I'm standing around with a sheet of paper. When it was my turn I promptly balled up the paper as tight as I could around a handfull of 1" steel washers and proceeded to throw the thing across the gym, out the doors and into the hallway outside, roughly 2x the distance covered by the closest competitor.
I was promptly disqualified for unspecified reasons.