Kvass is a soft drink that's fermented from black bread (rye).  It is popular among Slavic peoples and was the number one soft drink in Russia until Pepsi Cola moved in.  Initially, Soviet Russia bartered Stolichnaya vodka for Pepsi Cola concentrate because the ruble was worthless. 

By the late 1980s, so many Soviets were consuming Pepsi that it had eclipsed kvass as the favored soft drink but problems arose when the Americans began protesting the Afghan War - they stopped buying enough Stolichnaya to keep that barter deal viable.  So Pepsi and the Soviet Union made an arrangement where Pepsi would be the middle man in selling warships and submarines for scrap and leasing out tankers built by the Soviet Union.  This accidentally, temporarily made PepsiCo the sixth largest naval power.