A meal ticket is a ticket that entitles the holder to eat. “Meal ticket” has been cited in print since at least 1831, when it referred to the tickets given out on boats.
 
A “meal ticket” also means something or someone who makes money and figuratively “puts food on the table.” A baseball pitcher’s arm is called his “meal ticket” and a very good pitcher is called the “meal ticket” for his club. “A pitcher is very careful of his arm, as that member of his anatomy is his meal ticket” was cited in print in 1900. New York Giants pitcher Carl Hubbell (1903-1988) was called the Giants’ “meal ticket” by at least 1937. During 1936 and 1937, Hubbell set the major league record for consecutive wins by a pitcher with 24.
 
 
(Oxford English Dictionary)
meal ticket, n.
orig. U.S.
1. A ticket entitling a person to a meal, esp. at a specified place for a reduced cost.
1864 Harper’s Mag. July 234/1   The lodging is only ten, but you must pay for one meal also,..to secure it: you then receive a lodging ticket and a meal ticket.
1867 L. P. Brocket Woman’s Work in Civil War 542   A system of meal tickets, which were given to deserving soldiers of this class, entitling the holder to a meal at the depot dining room.
2. fig. and in extended use: a source of subsistence, livelihood, or income; something which ensures prosperity, financial security, etc.
Often implying some form of cynical exploitation, etc., as in a relationship in which one partner lives off the earnings of the other.
1899 ‘J. Flynt’ Tramping with Tramps 395   Meal-ticket, a person ‘good’ for a meal.
1912 Collier’s 23 Nov. 38/2   I’ve been doin’ a lot for her—a regular meal ticket an’ ticket agency for her.
 
29 November 1831, New-York (NY) American, pg. 2, col. 6 classified ad:
They furthermore swear that they have never, nor to the best of their belief and knowledge, has any person attached to the North River Line furnished any passenger with a meal ticket gratis, to induce him to take passage on board of said boats.
 
20 June 1834, Richmond (VA) Whig, pg. 2, col. 7 classified ad:
Those who hold Meal tickets from the Mill will send them in as formerly.
 
21 October 1900, Denver (CO) Sunday Post, “Floto’s Review of the Week in Sports,” pg. 18, col. 1:
A pitcher is very careful of his arm, as that member of his anatomy is his meal ticket.
 
Google Books
Forty Modern Fables
By George Ade
New York, NY: Harper & Brothers Publishers
1901
Pg. 66:
“All the Tin-Horn Sports and Shoe-String Gamblers speak of him as their Meal Ticket. He is put against a new Brace Game every Week. He is so Soft that sometimes even the hardened Sheet-Writers feel that it is a Shame to take it away from him. Butthey need the Vulgar Mazume, so they lighten him.”
 
Google News Archive
20 June 1937, The Telegraph-Herald (Dubuque, IA), “Hubbell Is Now Terry’s Worry,” pg. 16, col. 7:
New York—(INS)—No little part of Bill Terry’s success as manager of the Giants is due to the fact that Carl Hubbell has been his prize meal ticket for several years.
 
Google News Archive
3 April 1938, Tuscaloose (AL) News, pg. 10, col. 4:
“Meal Ticket” Hubbell
Giant Key Man Again
 
LA84 Foundation
1917, Baseball Magazine, “A Pitcher’s Day Dreams” by Ernest Shore, pg. 497, col. 2:
Most pitchers, however, are not thus gifted. They do not hope to developa delivery which will be a continual meal ticket.
 
Google Books
The Dickson Baseball Dictionary (Third Edition)
By Paul Dickson
New York, NY: W.W. Norton & Co.
2009
Pg. 538:
meal ticket A player of great imporance and reliability to his team, specif., a team’s winningest and most effective or dependable pitcher. Dizzy Dean once called St. Louis Browns pitcher Ned Garver a “meal ticket” because “he keeps ‘em eatin’ regular.” The player most closely tied to the term was New York Giants southpaw Carl Hubbell, who was known as “The Meal Ticket” not only because he kept the groceries on his manager’s table, but also because of his reliability between 1933 and 1937, when he won 115 games.