If you eat a lot of Vietnamese food, hopefully you'll know what I'm talking about. I think it's called "Uot" -- it is a round, translucent sheet made from rice, hard and plastic-y off the shelf, soft and elastic after soaking in water. They are used to make the cold spring rolls you can get as appetizers.
Sometimes they have a diamond-tread-like pattern on them.
Although they are fairly tough, and moderately water resistant, they could be made more competetive with petroleum-based blister packs by incorporating a mat o vegetable fiber.
The blister packs could be moulded with a channel around the edge, into which the user can pour a bit of water. The pack would then open much more easily than the welded plastic nightmares you currently have to rescue widgets from.
In addition to being biodegradable and non petroleum based, the manufacturing process could, I think, be cheaper, since water is the only chemical required. There is a potential benefit as well to animals and the homeless.