The lowest tech hack
Want to hack Apple's Itunes service to receive free songs? It's as easy as simply picking up a Pepsi bottle in a store and taking the time to look under the cap. According to an article on News.com, a little effort on your part, and you can not only see if the bottle is a winner, but you can also see the actual redemption code. Basically, at the very least, consumers can pick a winner to purchase, at the most they can rip off the full code.
Here's my idea of a low-tech solution for the Pepsi side (of course I am not a bottler and can't speak to the economic impacts of this idea, nor can I speak to how many bottles have been shipped or how hard it is to change the production lines): extend the length of the wrapper up the neck of the bottle.
As a side note: I wonder how many people would not have figured out this hack if it hadn't been reported?