"What is a duck's favorite…

A riddle about ducks and crackers is:

Q: What is a duck’s favorite snack?
A: Quackers (quack + crackers).

“Quacker Oats” has been cited in print since at least 1978, and “quacker”/“cracker” riddles have been printed in newspapers since at least 1982 and 1993. The joke has been printed on an image.

“What does a duck eat for breakfast?”/“Quacker Oats” is another duck “quacker” riddle.

4 February 1978, Star-Gazette (Elmira, NY), “Postmaster banks on his collection,” pg. 10, col. 4:
A third bank, presumably dedicated to Donald Duck’s favorite breakfast food, is in the shape of an oatmeal container and carries the inscription “Quacker Oats.”

9 January 1982, Indiana (PA) Gazette, “Mighty Funny’s Mini Jokes,” The Mini Page, pg. 3, col. 2:
Q: What is a duck’s favorite snack?
A: Quacker-jacks!
(All jokes sent in by Amy Garrett)

8 July 1993, Indiana (PA) Gazette, “Mighty Funny’s Mini Jokes,” The Mini Page, pg. 4, col. 2:
Q: What is a duck’s favorite snack?
A: Quacker-jacks!
(All jokes sent in by Amy Garrett)

9 September 1993, Gatesville (TX) Messenger, “You’ve Got To Be Joking,” pg. 9-A, col. 5:
What is a duck’s favorite snack?
Quackers.

28 December 1997, Los Angeles (CA) Times, “Sunday Brunch; Laugh Lines; Pint-Sized Punch Lines,” pg. E3, col. 4:
What’s a duck’s favorite food? Quackers. (Stacy and Denise Bernstein, 5, Torrance, Hickory Elementary)

Google Groups: alt.fan.dave_barry
Ducks Suffer From Squirrel Syndrome
Christin Keck
5/1/98
(...)
Old kid’s joke: Q. what is a duck’s favorite breakfast?
A. Quacker Oats!

18 June 2000, Los Angeles (CA) Times, “The Kids’ Reading Room; Reading by 9; JOKES & RIDDLES,” pg. E6, col. 1:
What is a duck’s favorite snack? Quackers. (Leah, 4, Toras Emes Academy, Los Angeles)

Google Books
The Little Giant Book of Giggles
By Charles Keller
New York, NY: Sterling Publishing Company, Inc.
2003
Pg. 85:
What is a duck’s favorite snack?
Quacker Jacks.

Twitter
Chris Campbell‏
@SoupInNYC27
What is a duck’s favorite snack food?
Cheese and quackers
11:22 PM - 21 Sep 2009

Google Books
Laugh-Out-Loud Animal Jokes for Kids
By Rob Elliott
Grand Rapids, MI: Revell
2012
Pg. ?:
Q: What is a duck’s favorite snack?
A: Cheese and quackers.

Twitter
Popsicle Jokes‏
@Popsicle__Jokes
What is a ducks favorite snack?
Quakers #PopsicleJokes
1:57 PM - 10 Apr 2016

“What is a duck’s favorite snack?”/“Quackers.”