The idea behind Google Wallet is that you can, theoretically, leave your wallet at home and pay with just a tap or wave of your smartphone. However, in reality, we're still a ways a way from that being the norm. Many places don't yet have tap and pay technology and still require you pay with cold hard cash or plastic. Google is apparently considering a physical Google Wallet credit card that you can use in stores that don't have tap and pay.
Android Police cites a tipster in reporting the card would be linked to the default card on your Google Wallet account and purchases would be charged to that. However, screenshots sent to the site say you can add multiple cards to the card (via the Google Wallet app) and then select the one you want to pay with in store. One card to rule them all, so to speak.
Additional features coming to Wallet include the ability to withdraw and deposit money from a Wallet balance, person-to-person transfers, and transit cards. While Android Police's source didn't say anything about when Google would launch these new features, he was able to order a Google Wallet credit card to his house via the app, so we'd say it's almost ready to launch. Stay tuned!