Related Clues:

• Caffeine source, often
• Output of some fountains
• Pop, elsewhere
• RC or Jolt
• Fountain choice
• Vending-machine offering
• Fruit juice alternative
• Gin fizz ingredient
• Scotch and __ (bar order)
• Scotch diluter
• Bubbly, brown potable
• Carbonated water
• Popular mixer
• Fizzy fountain fare
• Dark soft drink