How is regular shoping going to work if it takes a while to confirm? like you go to a supermarket with your phone and then pay, what happens if you have to wait to get it confirmed??
One way is off-blockchain transactions. So if then exchange had a deal to be a processor for the supermarket and you can send funds from your Exchange account so it all happens within the exchange. There could also be deal to use "green addresses" where your online wallet sending address is trusted by the supermarket. So if you sent funds from your exchange wallet and the supermarket trusts the exchange.