The possibility that we could be tracked not because we have a microchip implant but merely because we wear clothes, eat and carry objects around is real according to this article on C|net news.

A technology called RFID (radio frequency identification) consisting of miniscule microchips the size of a single grain of sand that listen to a radio query and respond by transmitting their unique ID can make this possible. Most RFID tags use the power from the initial radio signal to transmit their response and hence can be placed anywhere imaginable. Retailers are adoring this concept and soon everything more expensive than a Snickers bar will sport RFID tags making tracking possible through our own personal possessions. The privacy threat comes when RFID tags remain active once you leave a store and currently the RFID industry seems to be giving ‘mixed’ signals about whether the tags will be disabled or left enabled by default.”