Worst: Any supermarket card

The most common customer-loyalty card sometimes turns out to be the least beneficial, according to Consumers Against Supermarket Privacy Invasion and Numbering (CASPIAN). In the past decade, CASPIAN found that products sold at supermarkets with card-loyalty programs -- including Kroger ( KR) and Albertsons -- tended to be priced 28% to 71% higher than products at card-free competitors like Target ( TGT).

Consumer Reports also notes that customers can "can save big on this week's specials, but it's easy to blow all of your savings buying other higher-priced items while you're in the store."

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