I'm having trouble understanding how cash can be less convenient. You whip out $300 from the bank machine, and you can then make $300 worth of purchases, anonymously. And you can spend it anywhere, even with non-merchants.
Credit cards certainly have their place, but cash still works just fine in most situations.
Other than the anonymity factor, I fail to see how cash is more convenient. If you use a credit card, you skip the ATM visit, and the wait for the cashier to count the change. And the merchant doesn't have to count the receipts and make a visit to the night depository. Instead, the card company takes care of all that electronically. And you also get the obverse of the anonymity advantage: everything neatly tallied at the end of the month and sorted and categorized at the end of the year.