Sainsbury's was a supermarket chain on Earth.
Photographs of Polly Wright putting her shopping into her car outside Sainsbury's were published in magazines. (PROSE: That Time I Nearly Destroyed the World Whilst Looking for a Dress)
Other realities[]
In a parallel universe in which the Doctor had regenerated into a woman after committing suicide, she took a job at Sainsbury's as a trolley stacker while in hiding from the Time Lords on Earth in the year 2000. (AUDIO: Exile)
In the Daft Dimension, before attempting to initiating his regeneration, the Eighth Doctor took the time to thank, among other people who had helped him out in menial ways, the friendly counter staff at Sainsbury's for giving "service with a smile". (COMIC: The Daft Dimension 592)