Billboard vinyl is a hot new material due to its vibrant colors and material strength. These bicycle panniers are prototypes. They are designed to hold a large-sized grocery bag. There is a flap at the top to keep the baguettes dry. A panel at the back of the bag, closest to the bicycle keeps the bag from sagging. The panel is made from an old corrugated plastic campaign sign. Hooks and bungee cords at the back of the bag are for attaching to the bike rack and to keep the bag from bouncing around while cycling.
UPDATE: I showed these prototypes at the 1111 Independant Artist's Exhibition on Jan 11,2009. They got a good response. When I make some production ones to sell I think I will try seam piping for a professional-looking finish.
This is the same material I use to make wallets. There's several for sale on my Etsy shop.