On a regular bicycle - some poster board that tried to become a sail. As I recall, I somehow had it balanced across my handle bars and I discovered that I couldn't go very fast. But did not crash.

On a funky delivery bicycle (looked sort of like this: http://www.industrialbicycles.com/platform%20trike.htm)
- instead of a front fork and wheel, there's a large platform on two wheels, a reverse tricycle, and you TRIED to steer the whole platform.
So on this thing, I carried 5 gallon buckets of water with larval salmon. I was working at a large fish hatchery at the time, and we had an odd assortments of bicycles to get around.
I discovered that 1) the bike is hard to steer, 2) even harder on curves, 3) worse yet going up or down hills while making a turn. Some baby fish died as a result....