Someone can already walk around a grocery store and see what's in my cart or they can just watch me checkout. Buying groceries isn't exactly a private experience unless you buy your stuff online. Securing tags in things like a passport or credit card is important since identity theft is real and hardware to read the tags is cheap. Knowing what things I buy in the grocery store might help some marketers know what sells but I can't really think of any nefarious use of that kind of data.

Maybe you could use it to make some guesses about a person. An older guy buying frozen dinners, beer, and not much else is probably single or divorced. A woman buying prenatal vitamins is probably pregnant. Someone buying both Special K and Fruit Loops might have a family. But someone can already make these determinations from using their eyes. RFIDs might make it a bit easier but don't really add any new infosec facet to this grocery store experience.

> Someone can already walk around a grocery store and see what's in my cart or they can just watch me checkout.

The problem with electronic surveillance is never the surveillance part. It's the part where we can surveil billions of people at once without the need for billions of spies.

Of course it's trivial to tell. When individual items are tracked, it's exceptionally clear if the item is from the store or not.

Bring a Faraday's cage, or rather Faraday's bag. Use it once you've paid to store your goods.