“Brass band with a leader” was lunch counter slang for “pork and beans.” “Brass band without a leader” was slang for “beans” (without the pork).
   
“For instance, the succulent bean, the food of the demigods who people Boston, is known as ‘dynamite.’ When pickled pork is desired the combination is known as ‘brass band, with a leader’” was printed in The Daily American (Nashville, TN) on April 13, 1887. “‘Brass band, without a leader’ is a plate of beans without pork” was printed in the Brooklyn (NY) Daily Eagle on July 3, 1887.
 
The “brass band with/without a leader” restaurant slang terminology was rarely used after 1910.
 
   
13 April 1887, The Daily American (Nashville, TN), pg. 6, col. 6:
A BRAKEMAN’S DINNER.
Edibles by Names That Floored Even the Ubiquitous Reporter
Railway Reporter: ...
(...)
For instance, the succulent bean, the food of the demigods who people Boston, is known as “dynamite.” When pickled pork is desired the combination is known as “brass band, with a leader.”
 
Brooklyn Newsstand
3 July 1887, Brooklyn (NY) Daily Eagle, “Restaurant Calls,” pg. 13, col. 1:
“Brass band, without a leader” is a plate of beans without pork.
     
Chronicling America
15 July 1892, Dalles (OR) Weekly Chronicle, pg. 2, col. 4:
LIFE IN CREED. (Creede, CO.—ed.)
Table Fare and Affable Waiters—All Treated Alike.
From Harper’s Weekly.
(...)
One day a man ordered pork and beans for his dinner and getting tired of waiting he told the waiter to bring along the beans without the pork. The waiter stuck his head through a little cubby-hole at the rear end of the cabin and yelled to the cook: “Hustle along a brass band without a leader.” And the customer ate his beans without a leader.
 
Google Books
March 1896, Locomotive Engineers’ Monthly Journal, pg. 220:
... but the chances were you would select the longest name, such as a “brass band without a leader,” then you got beans; ...
 
15 August 1897, Dallas (TX) Morning News, “A Feature of City Life: The Restaurants of the Metropolis and the Familiar Places One Sees,” pg. 21, col. 2:
And then a New Englander with a taste for baked beans without the pork is made to blush. “Brass band without the leader!” covers his case.
 
Chronicling America
6 November 1897, The Evening Star (Washington, DC), “Waiters and Their Ways,” pg. 14, col. 5:
On the Bowery.
(...)
“‘One with the light out’ is his yells for coffee without milk and beans minus pork is ‘a brass band without a leader.’”
 
Brooklyn Newsstand
15 November 1902, Brooklyn (NY) Daily Eagle, “The Buckwheat of To-day,” pg. 12, col. 4:
This means that the buckwheat season has come around again, and that guests who have for months been ordering “one on,” “coffee in the dark,” “white wings, sunny side up,” “one dyspepsia in a snowstorm,” “beef an’,” “brass band without a leader,” “one wheat an’ one sweet,” “make it punkin,” “mystery without onions” and “plate o’ wheat” are varying the round of etymological gayeties by commanding the waiter to “brown the bucks.”
 
Google Books
Cassell’s Dictionary of Slang (Second Edition)
By Jonathon Green
Londeon, UK: Weidenfeld & Nicolson
2005
Pg. 175:
brass band with a leader n. [late 19C] (US) pork and beans; thus brass band without a leader, beans without the pork.