This saying, which does not necessarily pertain to either coke or fries, began with my nephew.
When my nephew was 2, his dad was establishing a transmission shop in southern California and his mom would often run parts for the store. My nephew KNEW that he was not allowed to ask for things and that asking was the surest way to get a "No". One day, his mom was very busy running parts and, to be honest, I think she sort of forgot he was in the back seat and had been there for a very long time, especially for a two year old.
Suddenly, inspired, he said "Somewhere there's coke and fries". Coke and fries is what he called all foods from a fast-food restaurant, much the same way all vegetables were "ho-hos".
Kindly note, he did not ask and yes, he did get some nourishment quickly.
It just warms my heart to know that these tidbits are not forgotten.