If you want to buy a beer at Flatstick pub in Seattle, don't whip out a $10 bill to pay—you'll walk away thirsty. Flatstick, a hot new mini-chain in the Pacific Northwest, doesn't take cash. Neither does Bluestone Lane, a coffee chain with locations in New York, Philly and D.C. Patrons there have to pay with plastic or an app called LevelUp. Want to grab a Sweetgreen salad for lunch with cash? No can-do at many locations.

Cashless commerce is popping up around the country, particularly in restaurants catering to a younger crowd, which is likely to leave home without any greenbacks, or even a wallet, and instead choose to live life with a smartphone and a few credit or debit cards attached.

Businesses who've gone cashless rave about the results. Flatstick owner Sam Largent told me plastic-only reduces error rates during times of complex accounting, such as calculating tips when shifts change.