Google Wallet is a super simple way to easily pay for stuff with a swipe of your phone and typing in a pin. Of course, not every single store has a terminal that works with Google Wallet, but with NFC built into more and smartphones, and Wallet already being available and ready to use on Android devices, it's a matter of time before that changes.
There's various security concerns with the technology, but considering the encryption involved both ways, it's not nearly as scary as some people may think. Announced at Google I/O, Wallet will be getting even more functionality. A new featured called Save to Wallet and appropriately called at that, will allow users to save offers from websites that are using the API. This will completely eliminate the need to deal with paper coupons.
The days of digging through ads and cutting out coupons, may eventually become a thing of the past. If you do save an offer to Wallet, it will actually remind you before it expires, that way in case you forget about it which is oh so easy to do. To take advantage of the offer, you can either show the offer code on your phone, or simply use Wallet how you normally would. This is pretty huge and will make it not only easier for consumers, but allow retailers to potentially reap more benefits i.e. sales.
Save to Wallet work with payment cards also as mentioned before. Works pretty much the same as with offers. You'll be able to get it off of a website and then put it into Wallet on your phone. The API is currently in closed beta and only approved partners will get access to the API.