you got my attention with that thumperclone.... !
For large loads I use a cargo net, front end hooks go onto the shiny metal shock mounts, back end hooks go to the back of the fender, or the 2 holes near the license plate if you don't want to scratch the paint on the fender...
Day-to-day tasks utilize an adjustable bungee cord, auto parts stores or walmart/target have them too. Ran about 7 bucks for a pack of 2, 24" I think at their shortest length, I hook them under the fender on one side, up and over the pillion seat (and cargo) and under the fender on the other side. I had good results with the stock IRC tire, but when I replaced with a Pirelli 140/90-15 on the rear, I had to relocate due to some rubbing - your results may vary - it may depend on your rear tire size and rear shock preload setting.
The 2 adjustable bungees work great holding down anything from a folded-up bike cover and rain gear, to a 30-pack of PBR, to a small suitcase.
-Pabst