Some pay for deli sandwiches with a flick of their Internet-enabled wristwatches. Osama Bedier waves his phone.

The customers who shop at Mollie Stone's Market, at the heart of this Silicon Valley city's startup row, are increasingly buying groceries without cash or credit cards.

"I haven't carried around cards for a very long time," Bedier said. "I try to travel very light."

These shoppers are still early adopting outliers - especially Bedier, the executive who ran Google Wallet before starting his own company to build mobile payment terminals - but Apple, Google and Samsung are counting on them as bellwethers in a new fight to become your inseparable virtual wallet. And despite early resistance from retailers and even consumers, momentum is now building toward making these tap-and-pay systems a widespread consumer habit.

Apple earlier this month announced enhancements to Apple Pay, which was introduced in the fall, and Google said it will soon launch Android Pay, its Google Wallet successor. Amazon dropped out of the digital wallet race earlier this year but could return. Samsung is about to enter the market after buying Massachusetts-based LoopPay in February.

"What's become the battleground for big tech companies is relevance: How do I become a crucial part of your life every day?" said Bedier. Making a purchase is "one of the few necessities you can't live without," he added.

Quietly waving and tapping a personal device to buy jeans or a burrito could one day become as ubiquitous as the old cash register "cha-ching," but tech companies must still overcome challenges before they can persuade consumers - and, just as importantly, the stores that sell to them - to phase out magnetic stripe cards in favor of "near-field communication," or NFC.