Mrs. PDXEbiker and I are big fans of Sunday Parkways; last year, she was an Intersection Hero for the SE version, and we had several family members from out of town join us for the other rides. This year, we're planning to volunteer even more. One of the great things about volunteering with them is that we've accumulated several Smart Trips tote bags; today I realized that a great use for a bag would be as a makeshift pannier.
I picked up a Bike Bucket kit from City Bikes ($12, though parts could be assembled more cheaply from a hardware store), reviewed the directions, and proceeded to convert. A sheet of plastic cannibalized from an old unused storage container served as a frame, and a couple of drilled holes and bolts later, and I was done. It's not a heavy duty pannier, and certainly not waterproof, but I think it turned out rather nicely -- and it shows my support for Smart Trips.
I encourage you to volunteer for Sunday Parkways; you may get a bag and soon be on your way to a fancy pannier like mine!