Credit cards are daily payment tools for many Americans, but yours probably also has unintended tactical uses you never thought of, such as slicing open birthday card envelopes your grandparents send.

Of course, credit cards offer convenience, and some also feature perks such as an interest-free period or rewards, the points or miles earned on spending. And if you pay your bill diligently — in full and on time each month — credit cards help build your credit rating.

But that’s the usual stuff. Many credit card accounts — and the cards themselves — can be used in strategic and sometimes surprising ways to improve your life.

1. LOCK IT DOWN. Most major card issuers have implemented “card lock” or “freeze.” It lets you turn your card off or on using the issuer’s website or app. You use locks to head off fraud when you misplace a card, for example. But you can turn the spigot off and on for other reasons, like curbing impulse spending or cutting off authorized users. And you might as well lock cards you rarely use in case the numbers are compromised.

Note that some uses of this feature don’t work well with American Express — its card freezes expire in a week.

2. USE “AUTOPAY” AND “EVERYDAY.” If you have multiple credit cards, designate one as an autopay card and use it for recurring payments. Carry a different card that’s “in the wild,” for everyday spending, whether in person or online.

At some point, that card will likely incur fraud — and after reporting it, you’ll get a replacement, but with this tactic, you won’t have to visit multiple sites to change your autopay details.

3. REQUEST A DOWNGRADE. If you have a seldom-used credit card with an annual fee, you might hesitate to close the account, which could lower the average age of your credit and affect how much total credit you’re using, both of which are factors in credit scores.

Issuers with many card options may let you switch to a no-fee card and maintain your credit line and credit history. That way, you ditch the annual fee without harming your credit.

4. PLAY THE GIFT-CARD SHUFFLE. Credit card rewards for specific types of spending are typically based on where you make the purchase, not what you buy. So if your credit card gives you outsize rewards for supermarket shopping, for example, you can buy gift cards for restaurants, retailers or home-improvement stores while you’re in the grocery aisles.

Exceptions may apply — for example, the supermarket may not allow you to buy gift cards with a credit card.

5. OPTIMIZE THE GRACE PERIOD. If you always pay your credit card balance in full but have a big purchase that will take weeks to pay off, consider timing it just right to maximize your grace period.

Make the purchase after your statement period closes. Then, you have about a month before the next statement closes, plus the grace period, which by law is at least 21 days. All told, that could be more than seven weeks of an interest-free loan.

Note: The grace period doesn’t apply to cash advances.

6. GO WITH TWO. Issuers would love you to use only their rewards card for all transactions. But one of the best tactics is to use two cards: one that gives you high rewards for certain categories of spending — such as 3% to 5% back at gas stations or restaurants — and another card that gives you good rewards on everything else, with “good” being 1.5% or 2% back. That way you reap substantially more rewards with the hassle of managing only two cards.

7. CALL AND YOU MAY RECEIVE. The card issuer’s phone number is printed on the back of your card, but it’s not only for reporting potential fraud or asking billing questions.

Make a mistake and get hit with a fee? Call and ask — nicely — for it to be waived. Use the same number to ask for lower interest rates or higher credit limits.

8. IN A PINCH, IT’S A TOOL. Credit cards, especially metal ones, can slice a lime, open a package or scrape frost off a windshield. They are a light-duty pry bar when fingernails won’t cut it and a better-than-nothing screwdriver.

If you damage the card, the issuer probably won’t object to replacing it. And expired plastic cards can be cut and repurposed in a number of creative ways, from collar stays to guitar picks.