If a ring is not personal enough for you, then the next step is getting the RFID chip implanted directly into your hand. There are even folks at hacker cons who will do that sort of thing for you ...

absorb electromagnetic signals from a hand-held reader using electromagnetic waves. The researchers say their new, less wasteful tags could help reduce the retail sector's reliance on RFID chips ...

[pc486] sent in his hack that uses an ATtiny85 to act like an EM4102, a chip used for RFID tags. Minimally, all that is needed is the AVR and a coil, but he recommends some filtering capacitors.