Grocery stores in the early 1900s functioned very differently than how they do today. One hundred years ago, a store was likely family-owned and customers had an account with the store. The selection would have certainly been more limited, and if you needed something special the owner of the store would need to order it for you and wait for it to arrive.
The supermarkets of today are mega-stores in comparison to what once was. Today everything from fresh meat to vegetables to cleaning supplies (and so much more) is available any time you want it. Today, customers pay each time as they leave the store, since now we shop in a variety of places and not always the neighborhood mom and pop store.