An employee in Perth, Australia, used the metallic package from a snack to shield his device that has a GPS and locate his whereabouts. He then went golfing... many times, during his work hours.
The tribunal found that the packet was deliberately used to operate as an elaborate “Faraday cage” - an enclosure which can block electromagnetic fields - and prevented his employer knowing his location. The cage set-up was named after English scientist Michael Faraday, who in 1836 observed that a continuous covering of conductive material could be used to block electromagnetic fields.
Now, if it works for his device, it should work to shield our credit cards as an RFID shield, don't you think? There's no reason to buy those expensive wallet or credit-card envelopes. Next time you have a Cheetos or potato chips, save those bags and wrap your wallet with them! :)