An old cry of the hot dog seller was:
 
“A loaf of bread, a pound of meat, and all the mustard you can eat!”
 
The seller would then cry out “Frankfurters!” or “Hot dogs!” and the price—“Five cents!”
 
The rhyme has been cited in print since at least 1897 and 1899.
 
 
Old Fulton NY Post Cards
20 June 1897, The Sun (New York, NY), “Athletes Honor the Queen: Sports of All Sorts Enjoyed by Britons at Ambrose Park,” pg. 9, col. 3:
... and Coney Island frankfurters sold by a gentleman who besought all comers not to go hungry when a pound o’ meat an’ a loaf o’ bread could be had, together with mustard, for a nickel, ...
 
Google Books
October 1899, The Junior Republic Citizen (Freeville, NY), “My Three Days at the Fair,” pg. 2:
“A loaf of bread,
A pound of -meat,
And all the mustard
You can eat.”
(...)
As soon as I got money I went to where they sold a loaf of bread, a pound of meat, and all the mustard you could eat, and got a frankfort and a little loaf of bread for five cents.
     
Old Fulton NY Post Cards
20 September 1903, Buffalo (NY) Courier, pg. 27, col. 5:
A loaf of bread,
A pound of meat
And all the mustard
You can eat!
They’re hot,
Red-hot dogs!
Coney Island sandwiches!!
 
The above familiar ditty is heard down the line during autumn fair time, and the “dogs” are pretty good eating, too.
 
Old Fulton NY Post Cards
4 November 1904, Daily Argus (Mount Vernon, NY), “Asbury Ladies Hold Annual Fair,” pg. 1, col. 5:
Here the hungry ones can get “a loaf of bread, a pound of meat, and all the mustard they can eat” In the shape of a roll and frankfurter, for five cents.
 
17 May 1908, The Sunday Herald (Boston, MA), “Beaches Ready to Receive City Folk,” Real Estate and Want Sec., pg. 1, col. 3:
There are restaurants where you can get anything to eat from a gorgeous course dinner to a “hot dog on a roll, a loaf of bread and a pound of meat, all for five cents.”
   
Google News Archive
16 September 1937, Reading (PA) Eagle, pg. 3, col. 2 photo caption:
—And All the Mustard You Can Eat
“A loaf of bread, a pound of meat, and all the mustard you can eat!” That traditional cry at the Reading Fair attracted William Larkin, of 1015 Elm street, who is shown here devouring one of those yard-long frankfurters. He has quite a job on his hands.
   
16 April 1960, Washington (DC) Post, “Chips Down, Instant Coffee Out, Peanuts in, 27 to Bag, at Stadium” by Dave Brady, pg. A8, col. 4:
“A loaf of bread (actually a freshly baked roll)...a pound of meat (really 1.6 ounces)...and all the (uncut and slightly hot) mustard you can eat…hot dogs!”
 
Google Books
Newsweek
Volume 79
1972
Pg. 77:
She sold hot dogs, singing out, “A loaf of bread, a pound of meat, and all the mustard you can eat.”
     
Google Books
Bringing Up the Rear:
A Memoir
By Samuel Lyman Atwood Marshall
Novato, CA: Presidio Press
1979
Pg. 3:
The hot dog, which had its genesis in that season (1906—ed.), was hawked door to door by peddlers who pushed bright steam carts and sang out: “A loaf of bread, a pound of meat, and all the mustard you can eat for one nickel,” a cry not heard since.
 
Google Books
The Way We Were:
Reflections from the 1930’s
By Betty Lou Wolfe Marian Jean Gray
Publisher: Worthington, OH: Renaissance Publications
1993
Pg. 17:
To draw attention to his food stand, he shook a long rubber wiener in the air as he called out, “A loaf of bread and a pound of meat and all the onions you can eat!! Five cents!!”