Google doesn't get any more info than the credit card companies already get. That is, the merchant name, merchant category code (e.g. "5411 grocery store") and amount. They have no idea what specific products were purchased.
So Google Wallet might record that I went to a McDonald's, or spent money at a hardware store... but the servers would have no data on what I bought.
Not exactly a big deal, especially compared to other services that we use, who know much more:
- Apple has more detailed info on all my purchases from their stores and iTunes.
- Amazon knows a lot about what I like to buy, and uses that info to give me suggestions.
- Ditto for eBay.
- Double ditto for CVS, Staples, my grocery store, and other places where I use loyalty cards almost every single day. (Heck, groceries know what toilet paper brand I use. Google has no such detailed info.)
The advantage to me is more targeted ads and coupons. The advantage to them is more sales. It's a win-win situation.
With Apple Pay, the banks always get our info on our transactions. That's not as benign. Whereas Google and merchants might use the info to serve us more pertinent search suggestions and ads and offers, the banks not only sell the aggregate data to ad agencies, but also analyze our purchases to see how our personal financial situations are going. How do you like that?