"A Chick-Fil-A in every pot!"
I had never heard of "a chicken in every pot" associated with McKinley.
In American politics, it is generally associated with Herbert Hoover's 1928 presidential campaign, although Hoover himself denied ever using it.
You are so right. McKinley was in the same vein, a “full dinner pail.” But it still boils down to “Eat More Chikun”