(You may have arrived here from Twists, Slugs and Roscoes: A Glossary of Hardboiled Slang, where “butter and egg man” is mentioned.)
Ken Yousten (firstname.lastname@example.org) sent me this passage from Texas Guinan: Queen of the Night Clubs, by Louise Berliner.
The El Fey Club, a hotbed for news and excitement. Even if the shows were the same every night, the audiences never were, nor the spontaneous entertainment. One night a man with a slow midwestern drawl came in and cheerfully began dispensing fifty-dollar bills to all the dancers. He bought everyone in the house a drink and made no fuss when he got the bill. Thrilled by this rare phenomenon, Tex decided that her guest needed a proper introduction. Leading the dandy to the center of the dance floor, at this time the size of a small white envelope, she signaled for a distinguished drum roll and said,
“Folks, here’s a live one, a buyer, a good guy, a sport of the old school, encourage him.”
There was applause and cries of:
“Who is he?”
“What’s your name?” asked Tex.
“Nix on the name,” said the unknown.
“What’s your racket, then?” queried the hostess.
“I’m a big man in dairy produce,” he muttered.
“That’s applesauce to this mob. I’ll send you right in,” and Tex shouted,
“He’s a big butter and egg man.”
Night after night, the big spender came in and ran up large bills. Everyone soon knew him as the big butter-and-egg man, and the expression quickly spread throughout New York. George S. Kaufman immortalized it by making it the title of a Broadway play about a rich midwestern sucker so free with his money that some smart Easterners take him for a ride.