Even without bio-metrics and facial recognition, grocery stores have been collecting a vast trove of information from customers, even those without "loyalty cards". And that data surely has value beyond the grocery business (insurers, drug companies, investors and even employers would be obvious consumers for the data). It seems that they probably use the data to target promotions and provide leverage with their suppliers, and investigate criminal activity, but once it becomes their data, there is not much/nothing you can do about how they use it, unless you live in CA and the store provides an opt-out method. We just have to rely on companies' image concerns, and possible ethics, to avoid having our data sold to whoever would buy it.
Given the influence of lobbyists and regulatory capture in this country, there is little hope that Americans will ever be able to reclaim their personal data with the force of law (I say their data, because the data stems from the choices we make to buy goods and services from the companies collecting it). It's true though that what we buy in stores will be used to market to us. That's a horse that has left the barn, but facial recognition in grocery stores just seems icky and intrusive. If you agree, you can find a list here of popular stores that do use, may use, or have pledged not to use facial recognition, and vote with your feet - or let them know how you feel.