I think problems like this are interesting, and I'm going to dump experiences in this post. Some of them even have pictures.
motorized 14' long projection screen - tied to bicycle seat and handlebars, did not attempt to ride bicycle. would have been uncomfortably heavy to carry a long distance.
all of my stuff. shopping cart and backpacking frame were essential. bungees and ropes useful also
some lumber for an attempt at a strandbeest. bungee'd to bike, rode, but was uncomfortable
two 12' 2x4s and some other assorted lumber - strapped to bicycle with inner tube and wheeled, did not attempt to ride.
~ 2'x3' sheet of stiff laminated honeycomb material, strapped to bicycle with inner tube, rested on pedal, did not attempt to ride.
11' section of unistrut. inner tubed to top bar on bicycle, rode successfully.
Large sections of willow log - hefted by hand truck and with the help of a friend.
Things that are useful:
bicycle inner tubes - make fantastic bungees
a large backpack - to put large things in, to strap larger things to. It's nice to have your hands free while walking, nicer still while you're biking.