This is a very cheap Hitch made with a swivel caster, a bracket for antenna poles and a piece of square iron pipe. To be fixed under the bike saddle. Great just because it allows the movement on three axes, so there's complete freedom while biking.
UC Merced Recycling and Sustainability has made a bike trailer out of a ladder! We use this daily to pick up loads of recycling around campus. It is a cool engineering project created by or own staff. Get to Zero Waste!