I grew up in Southern California in the 1960s and RC held its own with Coke and Pepsi.
I went to a local Middle Eastern restaurant + grocery to get some sweets for an Eid celebration at work (Diversity is still being celebrated for now).
While waiting for my order to be boxed up, I noticed that the cooler had RC/7-Up/Dr Pepper and a bunch of other brands I’d never heard of.
But the sign on the top of cooler was Pepsi. My curiosity piqued, no doubt because of this thread, and I asked the guy why they had RC etc.
He said because both Coke and Pepsi support Israel. I was skeptical, and asked two of my Muslim classmates. Apparently this really is a thing. How widespread I don’t know but there was apparently a campaign to boycott both Coke and Pepsi.
Forgive the digression. I’m sure the OP’s incident is not related.
I found some Reddit threads which suggest that, as far back as the '60s, the Chicago RC bottler/distributor specifically focused on getting distribution in local pizzerias; I also suspect that they focused on the mom-and-pop hot dog places, as I still see it in those, too.
For a long time it was Coke in Israel and Pepsi in the Arab world exclusively. This has apparently changed.
Growing up on Long Island in the 70s, more pizza places than not served RC.
2 posts were merged into an existing topic: 65 Mustang Trock Posts
A company called Coolbreeze, for one. Here’s their five-gallon bag-in-box syrups for cola, diet cola, and lemon-lime.
Here’s another company, Narvon, which makes an even bigger range of generic soda flavors, in syrup form, for restaurants.
Me neither, and I wondered about that too. Thanks for asking. (And thanks, @kenobi_65, for answering.)
Not quite.
The dialog is:
“You want a
Ccoke?”
“Yeah.”
“What kind?”
“Dr. Pepper.”
Lowercase “coke” is the generic regional term for “soda”. Like “kleenex” for “tissue” or “xerox” for “photocopy”. Uppercase “Coke®” is the trademark. Like Kleenex® and Xerox®. Of course that casing difference is very hard to hear in spoken dialog. 
But it is significant in written use, like on menu boards and such. Especially if accompanied by the Coca Cola trade dress. Likewise especially not if in lower case and no trade dress.
I grew up in Dallas in the 60s, same for both.
RC is a famous southern thing. RC cola and a Moonpie is a lunch special.
You can buy generic soda syrup for the fountain drinks at Sams club.
My Daddy always said bars use generic cola for their mixers.
Southern comedian Brother Dave Gardner used to talk about this combo pronouncing it
“Are oh see ko cola”
IME if you’re ordering a mixed drink with cola, they use generic liquor, as well.
Every Southerner knows “coke” is a generic soft drink. The brand is “Co-cola.”