Kodak has filed a patent application for edible RFID tags, or more specifically,
"A system for monitoring ingestion of medicine comprising: forming an antenna comprised of metal segments and said medicine; forming a digestible radio frequency identification (RFID) tag comprised of at least one of said antennas; ingesting said RFID tag; receiving signals and power from an external transmitter; transmitting signals from said RFID tag to an external receiver; and monitoring a signal from said RFID tag."
-- via Institute for the Future, New Scientist
They should be making these tags a required food additive. Then fitness clubs could detect that you've just lunched on three pork chops and beam guilt messages with your name on them.