Google just has rolled out the pilot for the so called Hands Free payment. Available at several selected stores in Los Angeles you just have to say “I would like to pay with Google” and the purchase is made via your Google account. Of course you must have your smartphone (which is going to be detected) with you and give the cashier your initials to verify your account and close the transaction. The cashier also is able to additionally check your Googles profile picture.
More Information: https://get.google.com/handsfree