Actually, Starbucks provides a service as all food service businesses do. Back in school a teacher in an economics class brought up a case where a man sued a restaurant that refused to provide him with any containers to take his leftovers home. The court ruled that restaurants provide a service, not a good, and that there was no requirement for them to provide him with any means by which to take unconsumed food home.
Assuming that precedent actually exists, you're paying for the service provided to you by Starbucks. Mind you, they intentionally provide the means by which to take the fruits of their service out of the facility as it makes a lot more sense business-wise, but you're buying being-served-coffee moreso than you're buying coffee.