One of the delightful facts about American English is that even though the rich regional variety of pronunciation and vocabulary ever diminishes, we’re still a long way from universal treatment of the language, and that’s an important detail for writers to observe. Take soda, for example. I mean pop. I mean coke.
Each of these three terms for carbonated beverages is prevalent in various parts of the United States, and the respective regional dominations aren’t likely to go flat soon. According to a Web site
Pop, however, is the dominant variant in terms of geographical coverage, popping up throughout the northern states outside New England and rarely elsewhere. Soda, by contrast, which accounts for a slim majority by population, is the term of choice in the Northeast, in and around Miami and St. Louis, in eastern Michigan, and in much of Northern California and Arizona. (This Northern Californian concurs, though I call carbonated beverages “soft drinks.” But I don’t drink them, so what do I know?)
Other, relatively rare synonyms are tonic in the Boston area and dope in some parts of North Carolina and South Carolina. (The latter term perhaps derives from the fact that originally, Coca-Cola contained cocaine — hence the brand name.) The dominant vocabulary in selected other nations includes “soft drink” for Australia and New Zealand (no, I’m not from Down Under), mineral in Ireland, and pop in Canada.
What does what you call a carbonated beverage have to do with writing? Whether you’re writing fiction or nonfiction, it behooves you to adhere to the local dialect, including vocabulary, when you’re engaging with regional culture. That’s easy for many authors, who write about their own neck of the woods and are intimately familiar with the local word-hoard.
But if you’re going to virtually venture afar in your writing, make sure your characters don’t stand out as strangers by the way they talk — unless, of course, that’s the point: A great strategy for showing, not telling, in a fish-out-of-water tale is to introduce the character by having them, for example, ask for a tonic when they sit down at a diner in the rural South.