Openledger and Bitshares have smart coins like bit.USD, bit.EUR that are pegged at the value of the fiat currency they represent. I guess Ocash will use them under the hood - you'll either hold a balance of those for spending or there would be some instant exchange to the smart coin from the asset you want to spend; the OCASH card will probably use visa or mastercard tech so it should be accepted at any regular POS.