This is a question that I've wanted answers too. So far, I've only seen some merchants accepting cryptocurrencies and quite complex for everyone to understand. It will get mainstream someday and by that time, everyone will just take out their crypto wallets and trade the currencies through their phones or some digital way. 

Now, I guess, the world has just shifted to cashless transactions. I have seen that in my country. 

Crytos are quite unstable at the moment i guess for it to be used. It can be worth less the next day or worth more. Imagine cash which fluctuates in the value.