Chameleon Networks has a plan for both reducing all that clutter in your wallet and making it a lot more difficult to steal your credit cards:
The Chameleon Card's black strip covers a programmable transducer that mimics the information on the magnetic strips of the cards it is replacing. A new handheld device from Chameleon, the Pocket Vault, programs the Chameleon Card to take the place of any credit card the consumer chooses for a transaction. Shoppers will be able to swipe their Chameleon Cards through the same magnetic readers used in stores and banks today. And instead of reading bar codes off the back of customer-loyalty cards, retail bar-code readers will scan the bar code displayed on the Pocket Vault itself.
We're not sure that carrying around a mini-vault is any easier than just carrying around a few credit cards, and besides which, a company called Privasys already had this idea years ago, and it wasn't as complicated or expensive as the Chameleon. Instead of the Pocket Vault you got one really thin card with a keypad, an LED display, and a reprogrammable magenetic strip that stored all of your credit card numbers (and could generate disposable ones). You just entered your PIN, selected the card you wanted, and you were set. Not sure whatever happened to this, but the prototypes we saw definitely worked.