Pack your plastic if you plan on buying a cocktail or a meal or watching a digital movie the next time you fly on Alaska Airlines.

Starting Aug. 5, the Seattle-based airline will no longer accept cash -- only credit and debit cards -- for in-flight purchases.

Visa, MasterCard and American Express cards will be accepted. Flight attendants will use a hand-held device to process the transactions, one that it's been testing on transcontinental routes for more than a year.

Alaska joins some other airlines including JetBlue and Virgin America in going cashless, a move the airlines say saves flight attendants from having to spend time making change and is more convenient for customers.

An Alaska spokeswoman acknowledged, however, that the policy could pose problems for those who don't have credit or debit cards.

"In Alaska, especially in some of the bush areas, people don't have credit cards," said Marianne Lindsey, manager of corporate communications. At least through the fall, the airline will sell $5 vouchers at ticket counters in Alaska for those who want to make onboard purchases.

"We'll see how it goes," she said. But anyone without a credit or debit card flying from anywhere else, including children, will have to come up with another solution, such as a Visa or MasterCard "money" card pre-loaded with cash, a card that usually requires an initial $3.50 to $5 fee to purchase.

Soft drinks, peanuts and pretzels are still free on Alaska flights, but the airline charges for beer, wine, cocktails, digital movies and packaged meals.

"If I were a parent," said Lindsey, "I'd pack my child a lunch."