Once a more-common benefit, few cards offer any protection against falling prices on already-purchased items, says Consumer Action's Ridout.

"Price protection is very rare to find but something nice to have if you buy something that you suspect the price to fall, like electronics," he says.

MasterCard will pay the price difference on a product if you find a lower price within 60 days of buying it. Capital One's Cash credit card, which is a MasterCard World card, also extends this same benefit to its cardholders up to $250 per claim. Cardholders can file a maximum of four claims per 12-month period.

Chase will refund the full difference between the price Sapphire cardholders paid for a product and a lower advertised price within 90 days of the purchase.

American Express, Visa and Discover don't offer price protection for your purchases.