Do they still sell a gallon of soda and do they sell cups still when I was a kid they did

Yes, they do.

They still sell both to my knowledge

As far as I know, they still sell the gallon of root beer soda. I am not sure if they still sell the cups.

Yes the root beer is still sold in gallons and half gallons. They sell souvenir mugs.

Yes

Yes they sell gallons! Not sure about the cups.

They still root beer in both half gallon and gallon sizes.

They sell collectable cups not sure if they sell gallons of soda though