“Spokane” (a city in the state of Washington) has been used in lunch counter slang for “pork and beans” since at least the 1890s and early 1900s. “The Pork and Beans’ club” (Spokane) was printed in the Seattle (WA) Post-Intelligencer on August 17, 1890. ““I learned that pork and beans is called ‘Spokane,’” was printed in The Oregon Daily Journal (Portland, OR) on March 17, 1904.
 
“‘Spokane,’ which means pork and beans, is allowed and is used from end to end of the country, because the sound of the expression and the exact order are so similar” was printed in the Tacoma (WA) Times on November 2, 1912. “Spokane” sounds, perhaps, like “po’k an’.” The “Spokane” term—like much of lunch counter slang—became historical by the 1950s.
 
     
Wikipedia: Spokane, Washington
Spokane (/ˌspoʊˈkæn/ spoh-KAN) is a city in Spokane County in the state of Washington in the northwestern United States. It is located on the Spokane River west of the Rocky Mountain foothills in eastern Washington, 92 miles (148 km) south of the Canada–US border, 18 miles (30 km) from the Washington–Idaho border, and 228 miles (367 km) east of Seattle along Interstate 90.
 
17 August 1890, Seattle (WA) Post-Intelligencer, “The ‘Kid’ a Pitcher,” pg. 2, col. 2:
The happiest lot of baseball cranks that have filed out of Madison street park this summer were those who gave vent to wild huzzas at the finish of yesterday’s game between the Seattles and Spokanes. Had not the manager of the Pork and Beans’ club openly asserted that Rockwell’s aggregation would win but one game in this series and that his own sluggers were invincible?
 
17 March 1904, The Oregon Daily Journal (Portland, OR), “Restaurant Talk Wins a Husband,” pg. 8, col. 5:
“I learned that pork and beans is called ‘Spokane,’ corned beef and cabbage ‘Irish turkey,’ and milk toast a ‘graveyard stew.’”
 
1 February 1909, The Daily Missoulian (Missoula, MT), “Rosie Tells of Freak Orders,” pg. 4, col. 3:
“Spokane” is the waiter’s code for pork and beans, while “Native Son” means coffee and doughnuts.
       
2 November 1912, Tacoma (WA) Times, “‘Inside Life’ On the Real Kitchen Slang Waiters Use,” pg. 3, cols. 4-5:
“Spokane,” which means pork and beans, is allowed and is used from end to end of the country, because the sound of the expression and the exact order are so similar.
 
Google Books
15 February 1911, The Mixer and Server (Cincinnati, OH), pg. 42, col. 2:
Spokane — Sounds like pork and beans, but is Siwash for a town in the eastern part of the State.
   
30 December 2007, The Spokesman-Review (Spokane, WA), “The Slice column: Pork and beans sounds pretty tasty” by Paul Turner, pg. ?:
Dec. 30—Slice reader Jerry Foulger was looking through a book on soldiers’ slang from World War II when he saw that, in certain military circles, “Spokane” meant pork and beans.
 
“Does pork and beans seem like a dish popular here or is there another level of meaning that we might be missing?” he wondered.
 
Well, Jerry, I don’t know about the 1940s. But I wouldn’t mind if the expression gained currency in 2008.
 
Just imagine.
 
“What kind of place is Spokane?”
 
“It’s great. No nonsense. It’s pretty and the people are genuine. It’s a pork-and-beans town.”
 
Google Books
War Slang:
American Fighting Words & Phrases Since the Civil War, Third Edition
By Paul Dickson
Mineola, NY: Dover Publications, Inc.
2011 (First printed in 1994)
Pg. 216:
Spokane. Pork and beans.