To “cry over spilt milk” is to worry about an unfortunate event that already happened (when it is too late to change the event). “Don’t cry over spilt milk. It could have been beer/gin/vodka/whiskey/wine” is a jocular drinking saying that has been printed on many images. “Never cry over spilt milk. It could’ve been whiskey” is said to have been a line from the character Bret “Pappy” Maverick on the television series Maverick (1957-1962), but it’s not known what episode this is from.
 
Other drinks have been used in the same meme. “Don’t cry over spilled milk… it could have been beer” was posted on Twitter on February 22, 2009.
 
 
Wiktionary: cry over spilt milk
Verb
cry over spilt milk (third-person singular simple present cries over spilt milk, present participle crying over spilt milk, simple past and past participle cried over spilt milk)
!. To worry about unfortunate events which have already happened and which cannot be changed.
     
Wikipedia: Maverick (TV series) 
Maverick is an American Western television series with comedic overtones created by Roy Huggins. The show ran from September 22, 1957 to July 8, 1962 on ABC and stars James Garner as Bret Maverick, an adroitly articulate cardsharp.
 
IMDb (The Internet Movie Database) 
Maverick (1957–1962)
Quotes
Bret Maverick: Never cry over spilt milk. It could’ve been whiskey.
 
TV Acres
Words of Wisdom
“Pappy-isms” - Sage advice often heard on the weekly installments of the western adventure MAVERICK/ABC/1957-62.
(...)
“Never cry over spilled milk… it could’ve been whiskey.”
 
19 August 1989, Calgary (Alberta) Herald, “Words of wisdom from the mouths of clowns” by Knight Ridder News, pg. E8:
I’d rather follow the learned ways of Pappy Maverick, who once blessed his card shark son, Bret, with a bit of folk wisdom: “Never cry over spilt milk. It could’ve been whiskey.”
 
Google Books
Uncle John’s Third Bathroom Reader
By Bathroom Readers’ Institute (Joyce L. Vedral)
New York, NY: St. Martin’s Press
1990
Pg. 144:
ON BOOZE
“Never cry over spilt milk. It could’ ve been whiskey.”
—Pappy Maverick, Maverick
       
Google Groups: rec.food.cooking
FAQ about computer recipe programs    
Sam Waring
9/16/94
(...)
... Never cry over spilt milk.  It could have been whisky.
 
19 March 1998, Calgary (Alberta) Herald, “Year of the Cowboy” by Karen Crosby, pg. B2:
Cowboy Wisdom
Never cry over spilt milk—it could have been whisky.
 
Google Groups: rec.music.gdead
Bizarre taping problem - any ideas? (NDC)
Rando0
2/5/99
(...)
“don’t cry over spilled milk, It could have been whiskey”~~Pappy Maverick
 
Google Books
The Prodigal Ones
By Mark Alan Colety
Lincoln, NE: iUniverse
2001
Pg. 121:
“It’s like my dad always says, ‘Don’t cry over spilled milk. It could have been bourbon.’”
 
Google Books
The Wee Book of Weegie Wit and Wisdom
By Ian Black
Edinburgh, Scotland: Black & White Publishing Ltd
2006
Pg. ?:
Never cry over spilt milk. It could have been whisky.
 
Twitter
Me Not Mai‏
@justshootmy
don’t cry over spilled milk… it could have been beer
10:25 PM - 22 Feb 2009
 
Twitter
The Simple Stencil‏
@SimpleStencils
Don’t cry over spill milk. It could have been wine.
http://www.thesimplestencil.com/
2:20 PM - 20 Mar 2009
 
Twitter
J D‏
@whatJD
#Möet tonight, people! Come out for a drink! http://www.theprivado.com/ “Never cry over spilled milk, it could have been vodka…”
1:28 PM - 12 Jun 2009
 
Google Books
The Quotable Drunkard:
Words of Wit, Wisdom, and Philosophy From the Bottom of the Glass
By Steven Kates
Avon, MA: Adams Media
2011
Pg. ?:
“Never cry over spilt milk. It could’ve been whiskey.” — “PAPPY” MAVERICK, MAVERICK
 
Google Books
Staying at Joe’s
By Kathy Altman
Don Mills, ON: Harlequin
2013
Pg. 127:
Don’t Cry Over Spilled Milk—It Could Have Been Beer.