"They were drinking prairie oysters"

Prairie oysters are non-alcoholic drinks typically served as a hangover cure the morning after a particularly boisterous night before. They consist of a raw egg, cracked open carefully so as not to break the yolk, served in a glass with Worcestershire sauce and hot sauce or ketchup and salt and pepper.

This cure appears in a number of other books, including the James Bond novel Thunderball, P.G. Woodhouse's short story Jeeves Takes Charge and Christopher Isherwood's Goodbye to Berlin.