Michael Miller, the owner of a Nashville, Tenn., bagel shop, refused to take credit cards for the first nine years he was in business because cash seemed so much simpler, but he finally relented last year.

"We had quite a few customers wanting to use credit cards," said Miller, 36, of Star Bagel Cafe.

As we march on to a cashless society, plastic is upping its value, becoming even easier to use.

In the amount of time it takes to reach into your wallet and whip out a $20 bill, you could wave a credit card in front of a sensor and be halfway to the exit thanks to several new "contactless" sensors showing up around Nashville. Even that's a snail's pace compared to what's being tested: payment information in your cell phone.

But are we ready for a world where anything can be had with a tap of a credit card or the wave of your mobile phone? As it is, consumer debt has been growing at an alarming pace.

And, if no one's carrying cash, what's the fate of the Salvation Army's familiar red kettles and the tip jars that performers depend on?

McDonald's restaurants in Nashville started taking credit cards about 18 months ago.

Another final frontier of cash use — the vending machine — is bowing to almighty plastic.

Coca-Cola has some 6,000 vending machines across the country taking credit cards. The machines accept anything you have: coins and cash, cards with magnetic strips and the new tech wave-and-pays, or "contactless" scanners, said Tristan Jordan, spokesman for MasterCard Worldwide.

People like to use smart cards in places where they're in a hurry and not spending tons of money: fast-food restaurants, drugstores and movie theaters.

More than 11 million smart cards are out there, said Randy Vanderhoof, executive director of the Smart Card Alliance, a New Jersey-based nonprofit that promotes secure digital transactions.

The next new thing will be using cell phones as mobile wallets in what's called Near Field Communication technology. People in New York City and Atlanta already are experimenting with it, Vanderhoof said.

You'd be able to load all your identity cards and the way you pay for things on your cell phone, he said. Imagine being able to embed into one tiny chip your gym membership, library card, grocery loyalty cards, video rental card and everything else you carry in your wallet.

So why do we love plastic so much?

"People prefer to make purchase decisions on the spot," Vanderhoof said. "They don't want to make choices based on how much money is available in their wallet. Once you start using your credit or debit card, it's a very freeing experience."

That worries Daniel Howard, chairman of the marketing department at Southern Methodist University's Cox School of Business in Dallas.

He fears even more bankruptcies and marital problems caused by fights over money. Americans already have run up non-mortgage debt of more than $2.4 trillion.

Whether shopping for a new pair of shoes or picking up goodies at the gourmet bakery, people buy more — and more impulsively — when shopping on credit, Howard said.

In Coca-Cola's short experience with credit-card-friendly vending machines, the soda maker found that people will purchase about 32 percent more — perhaps buying two sodas instead of just one, or selecting an expensive energy drink.

"Credit is not the enemy," said Susan Beacham, co-founder of Money Savvy Generation, which teaches families basic personal finance skills. "It's not knowing how to use it properly."