Hay and feed would have been intended for working animals and livestock, a century or more ago; flour, for their owners; and grain perhaps for both man and beast. The current business at this location also sells grain for human consumption, though only in the form of potent potables.
That business — yes, the liquor store — moved to its current mid-block location several years ago. Its old digs, now the site of a deli, still display faded signage (shown below) for a grocer that also may be of century-old vintage. The word at the bottom, partly obscured by the awning, might be "feed"; at the top, partially cut away by a punched-through window, could be the word "hostler" — a stableman.
Flour, hay, grain & feed
Surviving signage, 303 West 128th St. (Frederick Douglass Blvd.-St. Nicholas Ave.), Manhattan