I've been thinking about it, and I'm going with coin/card based. Gold/Silver(Gold being 100 silver) coins have long been the currency, but there are banks that do offer basically debit cards. Our food money will be put on a card every month, and all characters are welcome to have bank accounts so that they can carry cards instead of gold/silver. We will be paid by merchants for any loot we get in gold/silver though, so we'd have to go to the bank to deposit money.