Is there a formula for a Coke?

What does “kettle” mean when compared to a can of coke or a bottle of coke?

Why the patron in restaurant will use “a Coke” may not know how the restaurant serves Coke (do they serve it in a can or a glass or a bottle?). In both instances, people will understand you, but it is not “proper” construction.

What is the proper way to ask for an uncountable noun is to use “some” whether you are talking about Coke or ketchup, regardless if it comes in a fixed size. If you want to use the word “a”, you should specify the fixed size (e.g. What are the best substitutes for ketchup?