The AT24C02 is from Atmel's line of serial EEPROM chips with a whopping capacity of 2K! (256 x 8) That's not a whole lot more than the onboard EEPROM in an Arduino, but it does have the advantage of being external:

• it can stay in-situ even if the microcontroller disappears/gets exchanged
• multiple devices can share access

There are a few libraries available that encapsulate the interaction with external EEPROMs, but first step is a simple test of the basic read and write capability using the basic Wire library. Surprise, it just works (as long as you get your bits and bytes ordered correctly).

As always, all notes, schematics and code are in the Little Arduino Projects repo on GitHub.