a two cents plain 

A two cents plain is a glass of seltzer water. During the Great Depression, one could get an egg cream for twenty-five cents (seltzer, chocolate syrup, and milk), a chocolate milk (milk and chocolate syrup) for a dime, a chocolate soda (seltzer and chocolate syrup) for a nickel, or plain seltzer water for two cents. Two cents plain.

I'll have an egg cream for my lovely date, and I'll take a two cents plain.

a two cents plain by Judith June 17, 2006