Is money the appropriate unit?

  I think money is one of the most rational ways to exchange something, for example, wages or a salary for one's work, or a fare for bus or train, because it is ordinary difficult to barter what we want each other. However, today we can pay money by using IC cards, so the day when we do not have to carry cash will come someday. I think it is more rational to carry IC cards instead of cash to pay.