In English we have "countable nouns" and "uncountable nouns".
Countable nouns are used with a number or an article. "I have two books." "There is a book on the shelf."
Uncountable nouns are used with no indication of quantity, or with general words like "some". "I have some water." "There is water on the floor."
Either can be used with possessives. "Give me my book." "Give me my water."
All that said, uncountable nouns are sometimes used with a number or article when we mean one container of this thing, or one standard quantity.
So for example if you're in a restaurant where they have little packets of ketchup, "please give me a ketchup" would be understood to mean one of those packets. But you wouldn't say, "I like a ketchup on my hamburger", you'd just say, "I like ketchup ...". Well, maybe if you were trying to say that you like exactly one packet of ketchup, but it would be a very odd sentence.
If the ketchup is in a bottle, you would normally say, "I would like ketchup" or "I would like some ketchup." You could say, "Pass me the ketchup", meaning, give me the bottle. But you wouldn't say, "I am putting the ketchup on my hamburger", but rather, "I am putting ketchup on ..."
Likewise, "Please give me a Coke" means one can or glass or bottle.
Arguably this is leaving out assumed words rather than an alternate use of uncountable nouns. What you really mean is, "Please give me a packet of ketchup" or "Please give me a can of Coke".
I think you mostly hear this talking about food, but it is sometimes used for other things. If you were buying cans of fuel, you might say, "Give me two kerosenes and a propane." Etc.