A joke about salt and pepper shskers is:
 
Q: What did the salt say to the pepper?
A: Hey, what’s shaking?
 
The food joke has been cited in print since at least 1970.
 
“What did the salt say to the pepper?”/“Season’s greetings” is the same joke, but with a different punchline.
     
 
26 October 1968, Kenosha (WI) News, TV Telescope, pg. 9, col. 4:
Question: What did the salt say to the pepper?
Answer: Ain’t that gettin’ kind of hot?
Patty Gascoigne
6337 34th Ave.
 
Google News Archive
15 June 1970, Deseret News (Salt Lake City, UT), “Funtime Corner—The Riddle Box,” pg. 2B, col. 4:
What did the salt say to the pepper?
“Shake!”
 
23 February 1971, The Wayne Independent (Honesdale, PA), “News from the Wayne Highlands Elementary Schools,” pg. 4:
Here is a riddle. What did the pepper say to the salt? Answer (Shake)
Rose McDonald
   
Google News Archive
4 November 1974, The Free Lance-Star (Fredericksburg, VA), “Fun Time—The Riddle Box,” pg. 21, col. 3:
What did the pepper say to the salt?
You’re too shaky for me.
   
Google Books
Remember the A la Mode:
Riddles and Puns
By Charles Keller
Illustrated by Lee Lorenz
Englewood Cliffs, NJ: Prentice-Hall
1983
Pg. ?:
What did the salt say to the pepper?
“Shake, pal.”
 
Google News Archive
24 August 1985, The Free Lance-Star (Fredericksburg, VA), “Fun Time—The Riddle Box,” pg. 13, col. 2:
What did the salt say to the pepper?
“Shake!”
 
8 July 2001, Los Angeles (CA) Times, “The Kids’ Reading Room; Reading by 9; Jokes and Riddles,” pg. E6:
. What did the salt say to the pepper? You really shake me up! (Jodie, 6, McPherson Magnet School, Orange)
   
Google Books
Kids’ Silliest Riddles
By Jacqueline Horsfall
Illustrated by Buck Jones
New York, NY: Sterling Publishing Company, Inc.
2003
Pg. 9:
What did the pepper say to the salt?
“Shake, pal.”
 
Google Books
ROFL:
Rolling On the Floor Laughing Joke Book
By Sarah Perez
New York, NY: Tangerine Press
2005
Pg. 259:
What did the salt say to the pepper?
“Hey, what’s shaking?”
 
Google Groups: alt.humor.puns
Kids Puns of the Weak 02-08-05
Stan Kegel
2/8/05
(...)
What did the salt say to the pepper?
“Hey, what’s shaking?” (Taryn, 11)
 
Twitter
Corey Anderson
‏@coreyanderson
RT @mags2122 What did the salt say to the pepper? Hey Baby, what’s SHAKING [me: Mags gets “joke of the day” award in my book!]
4:58 PM - 6 Apr 2009
 
Twitter
Itai
‏@imperiumrex9
What did the pepper say to the salt? Hey, whats shaking?
2:12 PM - 14 Sep 2009