I've cut up my
ShopRite card about two years ago (though it's still annoying as hell being asked if I have one at the cash register EVERY FUCKING TIME). I think I spend maybe 5% more on my total purchases at the very most, probably less. I just ignore the potential savings and look at the real prices - if there are two stores nearby and one offers lower card-free prices (or same prices with less bullshit), that's the one I'd choose. This political activism is obviously 100.00% futile here in Soviet Jersey, but in libertarian places like Keene, New Hampshire it definitely could have an effect - if a lot of people raised privacy as a priority, then stores would find it in their best interest to phase out their customer tracking programs.
Some people may be scratching their heads and asking "why bother" -- after all, a quick glance at the receipt doesn't seem to reveal any personal information. Until you think about it in greater depth. The stores might not treating the accuracy of who's using the card very seriously (yet), but it's a stepping stone, and the same applies to how long the data is stored and whether it is shared with the government. On the most basic level, a store's database can tell the government that you were at the store at a given time. Fuzzy logic algorithms can be used to track your purchasing habits and help predict times when you won't be home, in case they're looking for a good time to bug your place or do whatever else the Stazi types do. But that unlikely scenario is just the tip of the iceberg.
What most people don't understand is how easily various databases can be integrated, and how much information can be obtained about your habits, your general psychological profile, and your mood, from the choices you make. The brief product identification on the receipt looks useless, but remember that the database actually stores the product ID's you bought, which can be linked to the stores inventory as a whole and even the nutrition information stored by the FDA. Government psychologists are just itching to try out speculative algorithms about your mood on that particular day... Why did you buy the less expensive cheese slices last week but went for the healthier choice this week? Etc. They will have a profile of typical grocery shopping habits of a terrorist one week before a suicide mission, and they'll be itching to put it to use! But it gets worse.
"Why does she never buy baby food or milk when her tax returns are showing 3 young dependents? Alert the CPS!"
"Why does he buy so much salted peanuts, for which there is a 73% statistical probability of being consumed with alcohol, when he indicated on a form that he doesn't drink? Alert the Health Insurance department!"
"This family's food budget does not correlate with their claimed income, trigger an IRS audit!"
Etc.