Or NFC it to their phone. I have my insurance cards on my phone. If the officer wants to do more than look at the phone while I hold it, he's going to need a warrant, until and unless the law is changed. (It's in the Constitution.) (Of course, they have passed voter ID laws to prevent voting fraud, when the numbers of Mafia hits in NYC exceeds the number of voting frauds the ID laws would prevent in the entire country in a year. It seems that "silly season" only stops when the legislature isn't in session.)
But no wallet? Sorry, but I pay my grandkids in cash. I can't see a 12 year old with a Google Wallet account. And SS cards? Medical insurance cards? AAA card? All on the phone?
Then your car breaks down, a cop stops and asks for identification and your phone crashes. Oh, you have a backup at home, but it's not going to do you any good - you're legally driving without having your license with you (which is required in every state). And AAA won't accept your word that you're a member, but can't give them your membership number. No thanks.