I'm cleaning up some old draft posts that I never wrote out. This one is even more relevant today then when I planned to write it.

https://www124.americanexpress.com/cards/loyalty.do?page=expresspay

http://www.engadget.com/2008/03/19/rfid-credit-cards-easily-hacked-with-8-reader/

http://www.difrwear.com/

I own a dirfwear wallet, and while it isn't perfect at blocking rfid tags at close range (3-4 inches) its a dam good walet and will stop distance and opportunistic sniffing. Like near a turnstyle or door frame. I met one of the creators at the last hope and played with a machine he had there setup for reading rfid cards at a distance.