"Everyone carried a shopping bag": Muriel Spark on London, 1945

This is from Muriel Spark's novel The Girls of Slender Means, which was published in 1963 and set in 1945:

These upper bedrooms looked down on the opposite pavement on the park side of the street, and on the tiny people who moved along in neat looking singles and couples, pushing little prams loaded with pin-head babies and provisions, or carrying little dots of shopping bags. 

Everyone carried a shopping bag in case they should be lucky enough to pass a shop that had a sudden stock of something off the rations.