For special occasions, both products change their packaging to appeal to consumers. They have both changed packaging for the olympics, during the holiday season, etc. to relate more to costumers. They use special imagery that symbolizes that event for that purpose. It will make a person want to buy the object for charity (if the companies decide to donate some money for each bottle sold). Such specialized packaging also creates the perception that that product is needed to make the event special. For example, Coke bottles with snowflakes on them make the holiday season seem more special, make it seem Coke cares about its customers and what goes on in their lives, and also that Coke is needed to make the holiday season seem truly like the holiday season.
My favorite packaging is done by Coke. It's such a classic logo and the same one has been used since I was born. It's been there throughout my life so it's familiar and cozy and classic whereas the Pepsi logo seems to be changing all the time; by the time I get used to one logo, it's been already changed. I like Coke bottles, too, for their familiar structure.
Pepsi should get a whole new marketing director. =)