It seems this is a desire of many, but we need to try to be realistic about bitcoin, a transaction with bitcoin simply takes too long at the moment while a transaction with cash only takes a few seconds, cash does not need anything except the other party to accept the cash you are carrying but with bitcoin you need a lot more than that, you need to have a device capable of sending bitcoin transactions and the other party needs a way to accept those payments as well.

Even if bitcoin became extremely popular there will be many places where it will be impossible to pay with bitcoin and you will still need to use fiat, so unless someone finds a way around that we will still need other forms of payment.