Supermarkets should shift to self checkout. I haven't queued for the past two years. The supermarket I buy my stuff has an app. You just scan as you pick, checkout from your phone and go your way. Also, they have self checkout stations.
Even if the money resides in the bank account, kama ako na mobile banking most banks have integrated with BUY GOODS so it can be done straight via the mobile app without moving money to the MPESA wallet.