I can theoretically leave my home with just my smartphone. I can use it to pay fare at the local train station, get directions to restaurants, read the news, pay for food and coffee, and even lock / unlock my apartment.

I do still bring my wallet and keys, because I'd hate to run into a scenario where my phone does get lost, stolen, or damaged, leaving me stranded without a way to get home. But the concept is definitely there, and for someone less paranoid than I, it's definitely possible to live a life of convenience.