Scarcity or shortages were rarely the reason for rationing during the war.
According to History.com, rationing was generally employed for two reasons: (1) to guarantee a fair distribution of resources and foodstuffs to all citizens; and (2) to give priority to military use for certain raw materials, given the present emergency.
At first, limiting the use of certain products was voluntary. For example, President Roosevelt launched “scrap drives” to scare up throwaway rubber-old garden hoses, tires, bathing caps, etc.–in light of the Japanese capture of the Dutch East Indies, a source of rubber for the United States. Collections were then redeemed at gas stations for a penny a pound. Patriotism and the desire to aid the war effort were enough in the early days of the war.
But as U.S. shipping, including oil tankers, became increasingly vulnerable to German U-boat attacks, gas became the first resource to be rationed. Starting in May 1942, in 17 eastern states, car owners were restricted to three gallons of gas a week. By the end of the year, gas rationing extended to the rest of the country, requiring drivers to paste ration stamps onto the windshields of their cars.
Butter was another item rationed, as supplies were reserved for military breakfasts. Along with coffee, the sugar and milk that went with it were also limited. All together, about one-third of all food commonly consumed by civilians was rationed at one time or another during the war. The black market, an underground source of rationed goods at prices higher than the ceilings set by the Office of Price Administration, was a supply source for those Americans with the disposable incomes needed to pay the inflated prices.
Some items came off the rationing list early; coffee was released as early as July 1943, but sugar was rationed until June 1947.