To a growing number of youths, a wallet stuffed with cash and cards is as unfashionable as the millennial tuck, no-show socks and skinny jeans. Carrying only a smartphone is the way. Iykyk — that’s “if you know, you know,” for those who don’t know.

I, Brian Chen, a graying 39-year-old tech columnist, am not one of those in the know. It’s unfathomable to me to part with my wallet, which holds crucial items like my driver’s license. So in an effort to be hip again, I recruited my 23-year-old colleague Yiwen Lu to ask the young ones how they live like this, and then I took the jump myself.

In ditching my physical wallet, I am joining youths like Ruby Hegab, a 19-year-old student in Fremont, Calif. As soon as she got her first credit card last year, she said, she went all-in on using her iPhone to pay for groceries, parking meters and restaurant meals, and for carrying insurance cards.

“If a store doesn’t accept Tap to Pay, I won’t give them business,” Ms. Hegab said. But that rarely happens, because the overwhelming majority of merchants she visits, including big box retailers and mom-and-pop shops, now accept some form of mobile payment from services like Apple Pay and Venmo.

In a survey asking just over 2,500 Americans about digital payments, some 80 percent of Gen Z respondents said they were using mobile wallets, and among them, half were eager to use their phones for much more than paying for things, according to recent data from Pymnts Intelligence, a research firm that studies commerce.

Younger people are increasingly using their phones for purposes that older adults would use a traditional wallet for, like carrying documents such as a driver’s license, boarding passes and event tickets. Some of these digital items can be added into the Apple and Google wallet apps, while others, like insurance cards, can be downloaded through third-party apps.