This propaganda poster is a bit unusual for several reasons. For one, it does not actually feature a particular foodstuff. For another, the reason for this poster is the result of a very unique time period in American history.
For most of the 19th century and into the early 20th, if you wanted to keep food cold, you had to harvest natural ice on a pond, lake, or river, store it in an ice house packed with straw or sawdust, and hope that enough of it survived the spring, summer, and fall for you to keep your ice box well-chilled with enormous blocks of ice. If you lived in an urban area, the ice man would deliver weekly a giant block of natural ice to help keep meats, milk, and leftovers adequately chilled to prevent short-term spoilage.
By the time of the U.S. entrance into the First World War, artificial refrigeration was on the rise, and frozen food storage and refrigerated rail cars were new and effective technologies.
However, artificial ice production, advertised as more pure than natural ice, which often came from polluted rivers and lakes, required ammonia to produce ice. But ammonia was also used to produce munitions, and during the war a shortage ensued.
The harvest of natural ice was encouraged to assist with the shortage and ice was promoted to prevent food waste from spoilage.
Following the war, the spread of electricity led to the increasing popularity of electric refrigerators. Present before the war but enormously expensive, by the 1920s they were approaching ubiquity in the nation's urban areas.