How it often works: Buy something that comes with a manufacturer's warranty and the card issuer will extend that warranty, usually for one extra year.

This benefit is great for large or expensive buys, such as washing machines, computers and home electronics. However, you might not realize that it often applies to anything that comes with a warranty, such as eyeglasses, blenders, coffee makers, luggage and furniture, says Elizabeth Crosta, director of public affairs for American Express.

Frequently, consumers only learn about this perk if they've had an issue, she says.

Some issuers will cap the coverage at a certain point in time, which is often five years. For example, if your new TV already has a five-year warranty, you won't extend the warranty by using your card.