After watching Dean Collins portrait lighting DVDs I ran out to the Garage last Sunday afternoon and built a set of light panels out of 3/4" PVC and ripstop nylon. These are not small, measuring in at 52" X 82", but they beak-down easily for transportation. I was able to build two (2) panels for about $20 in PVC and $30 in fabric. You can get the plans for these "tinker tubes" here, thanks to the Strobist for the link.
I decided to take them out on location for a shoot in afternoon sunlight as a diffusion and reflective light source. The first picture posted is a set-up with the translucent panel to camera right and reflective panel to camera left. Sunlight is the only light source and is from camera right. As you can see from the image this set-up creates soft wrap-around lighting, which is very flattering to the subjects. One other consequence of screening the direct sunlight is a brighter background as the exposure must be adjusted for the lower light levels on the subjects.
As you can see from the picture I ended up placing my camera bag on the reflector panel for stability. (it's not nice to drop lighting gear on you customers while shooting...)
Go out and have some Fun!