The answer is:
Chewing Gum
The United States military have regularly supplied soldiers with chewing gum since World War I because it helped both to improve the soldiers' concentration and to relieve stress. In 1935, an estimated 12,000 lb was chewed in one month. As of 2005, the U.S. military is sponsoring development of a chewing gum formulation with an antibacterial agent that could replace conventional oral hygiene methods in the battlefield. This product is not expected to be available for use for some time to come.