Commissaries, which are operated by the Defense Commissary Agency, or DeCA, are supermarkets, often called exchanges, and are usually located on or near military bases. The stores sell groceries, cleaning supplies and other items, such as clothes, at cost plus 5 percent. This can help save members of the military, as well as other authorized individuals, money on living costs. Not just anyone is allowed to shop at a commissary, however.

Active-duty Members of the Military

Any active-duty member of any branch of the military, including Army, Marines, Navy and Air Force, is permitted to shop at any commissary in the United States. While active-duty members are also permitted to shop at international commissaries, the rules regarding bringing the items back to the United States vary, according to the DeCA, which also notes the commissary privilege is substantially restricted and will vary from country to country, depending on agreements with the host country. Active-duty members must show a valid and current military ID to shop in the commissaries, both in the United States and abroad.

Guard and Reserve Members

Guard and reserve members are also permitted to shop in commissaries. This benefit encompasses any commissary in the United States, Puerto Rico and Guam, according to the DeCA. Any member of the Ready Reserve, Selected Reserve, Individual Ready Reserve and the Inactive National Guard are included in this benefit.

Retired and Disabled Individuals

Members of the military who have retired retain their rights to shop at commissaries. This includes "gray area" retirees -- those who retired from the military but have not yet reached 60. These retirees have unlimited use of commissaries in the United States, Guam and Puerto Rico; the rules overseas depend on agreements with host countries. Veterans who are 100 percent disabled in connection with their military service also have the right to shop at commissaries.

Medal of Honor Recipients

Those who are discharged before service that continues through retirement do not retain their rights to shop at commissaries unless they have been awarded the Congressional Medal of Honor or are 100 percent disabled because of their service, according to DeCA. These individuals retain the right to make purchases at commissaries in the United States, Guam and Puerto Rico.

Authorized Individuals

Immediate family members of active-duty service members, reservists, retired members of the military, disabled individuals and those with a Medal of Honor are authorized to shop at commissaries with the appropriate ID. A named person, who may or may not be related to someone authorized to shop at the commissary, can shop for an authorized person with appropriate permission and identification, according to the Department of Defense. This can occur if the authorized person is disabled or otherwise can't shop for himself. In emergency situations, such as a natural disaster, the Department of Defense can authorize temporary access to commissaries for civilians in order to maintain quality of life. In many cases, diplomats and other persons serving at U.S. embassies overseas can shop at commissaries in the host country.