A ‘honeymoon salad,” as the old joke has it, is “lettuce alone” (“let us alone”). “Honeymoon salad” (“lettuce alone”) is cited in print since 1925. By the 1970s, a “honeymoon salad” acquired the added description of “lettuce alone and no dressing.”
   
The London humor magazine Punch had written in 1856 a widely reprinted joke that “Salad for the Solitary” is “lettuce alone.” A 1924 newspaper published a recipe for a “honeymoon salad” of pineapples, Maraschino cherries, pistachio nuts, almonds, marshmallows, oranges, peaches, and lettuce, but “honeymoon salads” composed of anything besides “lettuce alone” are rare.
 
   
Everything2.com
honeymoon salad
(recipe) by in10se
Wed Mar 31 2004 at 21:57:59
Ingredients
. Lettuce alone.
. No dressing.
 
Google Books
A Dictionary of Slang and Unconventional English
By Eric Partridge and Paul Beale
Routledge
2002 (Eighth edition)
Pg. 565:
honeymoon salad. lettuce; joc.; C.20. “Let us alone!”
 
Google Books
25 October 1856, Punch, or the London Charivari, pg. 170, col. 2:
TWO LITERARY SALAD-BOWLS.
“Salad for the Solitary”—Lettuce alone!
“Salad for the Social”—Lettuce be merry!
   
12 November 1856, Lowell (MA) Daily Citizen and News, pg. 2:
Two Literary Salad-Bowls.
“Salad for the Solitary”—Lettuce alone!
“Salad for the Social”—Lettuce be merry!
   
10 April 1924, Trenton (NJ) Evening Times, pg. 9:
Honeymoon Salad—Open two cans of pineapple, cut in small pieces, place in large salad bowl and add: Two large bottles Maraschino cherries, cut in small bits and drained well. Quarter pound of Pistachio nuts cut in bits. Half-pound of almonds, blanched and cut in thin slices. One pound of marshmallows, cut in small pieces. One small pot of preserved ginger, cut in small pieces. Remove the skin from 12 oranges and with sharp pair of scissors, cut the orange pulp in small pieces. One can of peaches cut in small pieces. Mix; then turn in nests of crisp lettuce and serve whipped cream; garnish with flowers made from thin slices of strawberries, then dust with powdered sugar.
       
29 April 1925, Mitchell (SD) Evening Republican, crossword puzzle, pg. 11:
This vegetable alone makes a honeymoon salad
(Seven letters—ed.)
 
27 June 1925, Rushbille (IN) Daily Republican, pg. 4, col. 6:
Honeymoon Salad
Sam Trabue is telling a good story on himself which relates to an experience he had recently in Chicago while there on business relative to the office of major general of the Uniform Rank, Knights of Pythias, in the United States and Canada.
 
When Mr. Trabue consulted the menu while at lunch, he discovered “honeymoon salad” and he ordered it. The waiter brought a thin leaf of lettuce.
 
“Look here, George, said Mr. Trabue. “I ordered honeymoon salad and this is just plain lettuce, not even head lettuce.”
 
“Yes sah, boss,” answered the waiter with a broad grin, “dat am honeymoon salad. Lettuce alone.”
     
21 February 1926, Dallas (TX) Morning News, sec. 3, pg. 2:
“Lettuce Alone.”
Oil Weekly: “Send up two portions of salad to the bridal suite.”
“What kind of salad do you prefer?”
“Lettuce alone.”
 
15 September 1926, Logansport (IN) Morning Press, pg. 4, col. 4:
She Knew Something
The obviously newly-wedded pair had stopped to get some light refreshment. A trim waitress approached them and politely asked if they wanted honeymoon salad. The bashful and puzzled bridegroom asked of what it consisted.
 
“Just lettuce alone,” replied the waitress.
 
Google Books
Key Note
By Key System Transit Lines (Calif.)     
v. 3
1927
“Honeymoon Salad: Ingredients — Lettuce alone.”
     
Google Books
Mixer and Server
v. 38
1929
Pg. 29:
“Some honeymoon salad, please.”
“You have me there, sir,” replied the manager. “May I ask what it consists of?”
“Just lettuce alone.”
 
15 March 1930, New Orleans (LA) Times-Picayune, pg. 17:
Each of these broadcasts is considerably akin to a big-time vaudeville act. The lines are put across fast. And they register usually—though the Raybestos Twins’ gag Friday about honeymooon salad (just lettuce alone) has been a favorite for many moons with the lads and lassies who work in cafes in New Orleans, New York and at the forks of the creek.
   
Google Books
The American Magazine
v. 144
1947
Pg. 97:
Young couple: ‘We’d like a honeymoon salad.’
Waiter: ‘A honeymoon salad?’
Couple: ‘Yes; lettuce alone.”
 
Google News Archive
12 December 1977, Village Voice (NY), “Counter Code,” pg. 60:
Honeymoon salad: No dressing on this salad.
(...)
3. A honeymoon with Tommy; bring the radio in a monkey dish.
Answers
3. Plain lettuce and tomato with a side plate of tuna fish.