I drink a lot of coffee, although not usually from Starbucks. But my characters go there. That's because it is a nationally-recognized name, and I like to use some recognizable brands to give my stories a sense of authenticity.
But I know writers who are scared of using brand names. They think it will violate copyright or trademark laws, or they don't want to use the ® symbol because it can interrupt the flow of the story.
I don't worry about any of that.
You can't copyright names, so copyright law doesn't apply. You can trademark names, and Starbucks is a registered trademark. However, trademarks have a specific, limited purpose, so the protection the owner gets is much narrower than with copyrights.
Trademarks protect against consumer confusion over the source of a product or service. Consumers use recognizable names and symbols to tell them that they are getting a certain quality or a product with particular characteristics. When you see the Nike swoosh on a pair of shoes, you expect them to last for a while. When a counterfeiter prints the swoosh on shoddy-quality shoes, people are mislead. That harms both the consumer (who is not getting what he or she expected) and Nike (who could lose sales to the counterfeiter and suffer harm to its reputation when the shoes fall apart).
Your characters can drink 7-Up without worrying about trademark infringement. No one is going to go out and buy counterfeit 7-Up based on your novel, nor will readers assume that the makers of 7-Up are connected with your book. You don't have to call it lemon-lime soda.
A brand name can lose its trademark protection if consumers use it generically for any brand of the same type of product. After people started referring to all tissues as kleenex and to photocopies made on any brand photocopier as xeroxes, the owners of those trademarks spent a lot of money educating consumers on the proper use of the terms. That's why brand owners would like you to use the ® symbol. But you aren't required to. If you want to help trademark owners protect their property and you think "the real thing" will add authenticity, just capitalize Coke.
So let your characters drink Starbucks' coffee if they want to. Or 7-Up. Or Coke. (There seems to be a lot of drinking in this post. Maybe I should send my characters to the bathroom more often.)
Kathryn Page Camp