bugsy wrote a review of Pacific Outdoor Equipment Pneumo Dry Bags on September 11, 2006
I use a set of these bags as luggage on a small motorcycle. A 5-liter bag goes each side of the tank, in front of my knees; a 25-liter bag hangs on each side of the passenger seat.
They're light, waterproof, and compressible so they don't stick out much. They're also bright orange for visibility.
They work great, but don't overload them; the roll-down tops can open up if not rolled carefully with at least three turns. I'm satisfied. Versatile, waterproof packs for my bike at a quarter of the cost of motorcycle luggage.