It's a bit gimmicky, sure, but the idea of adding a copy of the US Constitution to your iPod holds a certain appeal. The American Constitution Society for Law and Policy is making the Constitution available as an iPod "Notes" file (which, sadly, doesn't work with the ancient first generation iPods -- sorry, early adopters, like me) for easy portability and quick reference. One wishes that certain members of the current administration had a deeper familiarity with the text; perhaps this will help.
Of course, you can turn any text file into an MP3, generated by high-quality text-to-speech, using TextAloud. And since the Constitution is a public domain doc available from Project Gutenberg or Bookshare.org, getting an ASCII copy should only take you a minute! You won't have any navigation capability within the MP3, unless you break the Constitution down into sections, but you can get it to your iPod in no time nonetheless.