A Halloween ghost pun on shredded wheat is:
 
Q: What do ghosts eat for breakfast?
A: Dreaded wheat.
 
The joke has been cited in print since at least 1983. “What do ghosts eat for breakfast?”/“Ghost Toasties” and “What do ghosts eat for breakfast?”/“Scream of Wheat” are a similar breakfast riddles.
 
“What do ghosts eat for lunch?”/“Boo-logna sandwiches,” “What do ghosts eat for lunch?”/“Spookghetti,” “What do ghosts eat for dinner?”/“Ghoulash” and “What do ghosts eat for dessert?”/“I scream” are related Halloween riddles.
     
 
Wikipedia: Shredded wheat
Shredded wheat is a breakfast cereal made from whole wheat formed into pillow-like biscuits. It is commonly available in three sizes — bite sized (¾×1 in), miniature (nearly half the size of the bite-sized pieces), and original. Both smaller sizes are available in a frosted variety, which has one side coated with sugar and usually gelatin. Some manufacturers have produced “filled” versions of the bite-size cereal containing a raisin at the center, or apricot, blueberry, raspberry or cranberry filling.
   
Google Books
October 1983, Boys’ Life, “Think & Grin,” pg. 82, col. 2:
Casper: What do ghosts eat for breakfast?
Jasper: I don’t know. What?
Casper: Dreaded Wheat. — Nathan L. Sandland, Gilroy, Calif.
   
Google Books
November 1998, Boys’ Life, “Think & Grin,” pg. 61, col. 1:
Bob: What’s a ghost’s favorite breakfast cereal?
Rob: What?
Bob: Dreaded wheat! — Jeffrey Liang, Alhambra, Calif.
     
Google Books
The World’s Scariest Joke Book
By John Byrne
New York, NY: Puffin Books
2001
Pg. ?:
What do ghosts have for breakfast?
Dreaded Wheat.
Sarah-Jane, 8
 
22 March 2003, The Guardian (UK), “How to tell jokes” by Guy Browning, pg. C10:
Most normal people can ever remember one joke and it’s usually something fantastically unfunny such as, “What do ghosts eat? Dreaded Wheat.”
 
Google Groups: alt.creative.writing
What does a ghost eat?
omjaram
10/21/04
(...)
I know you won’t be able to resist goblin up this full-corpse meal. Bone appetit!:
 
Grains
Ghost Toasties      
Scream of Wheat
Pentagram Crackers with Poisonbury Jam      
Brain Muffins
                     
Entrees
Hungarian Ghoul Ash  
Frank ‘n’ Stein
Stake Sandwitch      
Halloweenie
Grave-y
Littleneck Clams      
Black Catfish
Warlocks and Bagels, with Scream Cheese      
                     
Side Dishes
Spook-ghetti          
Deviled Eggs
Artichokes            
Skullions
Scarrots                
Ghost Liver Pate
                   
Fruits
Adam’s Apples          
Nectarines
                   
Desserts    
I Scream
Boobury Pie              
Boo Meringue          
Ghoul Whip
Terrormisu            
Ladyfingers
Ghoulda Cheese        
Monster Cheese
                     
Beverages
Ghoul Ade
Coffin with Scream
Zombie
Apple Spider
         
Google Books
Penguin Pocket Jokes
By David Pickering
New York, NY: Penguin Books
2006
Pg. ?:
What do ghosts eat for breakfast?
Dreaded wheat.
 
What do ghosts eat for lunch?
Spooketti.
 
What do ghosts eat for dinner?
Ghoulash.
 
Twitter
This Guy
‏@imperiumrex9
@Dritaa What do ghosts eat for breakfast? Dreaded wheat.
7:24 PM - 24 Jul 2009
   
Google Books
The Funniest Spooky Joke Book Ever
By Joe King
London: Anderson Press
2011
Pg. ?:
What do ghosts eat for breakfast?
Dreaded wheat
 
What do ghosts drink at breakfast?
Coffee with scream and sugar.
 
What do ghosts eat for lunch?
Ghoulash
 
What do ghosts eat for dinner?
Spook-ghetti
 
Google Books
More Cool Ghoulish Jokes For Kids
By Peter Crumpton
PeteyRF Creative
2015
Pg. ?:
What do ghosts drink at breakfast?
Dreaded Wheat.