Making a plastic card that looks like a credit card with a long-range module inside
If your goal is to make some sort of tracking device that you could find somewhere further than you could throw a ball, RFID and BT are out.  

You could take the components commonly found in cell phones and boil it down to only what matters for this application: a GPS module and a cellular radio.  Both could be made quite thin, the limiting factor would essentially be PCB thickness, IC height, RF shielding, and battery.  To access anyone's cell network you will need a SIM card or other method for them to bill you.

Be aware that designing a circuit to be thin (let alone credit-card thin) and with a high level of integration is a very difficult and very costly problem.  There's a reason a Droids and iPhones cost $500+, even when sold by the millions.