Assuming that supermarkets start to accept bitcoin as an alternative payment for their products, they must first solve the problem about the transaction speed with regards to the payment.
Every time you transact using your bitcoins, each spends relatively 8-10 minutes per transaction which makes it timely for most individuals, resulting to clogged and long lines. Next, when businesses use bitcoin as an alternative payment, every transaction also includes a fee for miners which again, is costly for the side of the business. Lastly, the volatile price of bitcoin can be a boon or a bane to the business and to the consumer as bitcoin does not have a stable price to begin with.

I doubt that supermarkets will accept bitcoin as an alternative payment soon but once the aforementioned problems have been solved, then large supermarkets and other services as well may come into the picture and accept it as an alternative payment.