For what it's worth, I've had a few experiences overseas where I (or someone in my group) accidentally insulted someone by leaving too large a tip. While my initial reaction was to agree with the "our cultural faux pas is their extra couple of bucks," I can definitely appreciate the fact that it can come off as condescending to throw (figuratively) extra money at someone for doing their job. I think part of not being an "ugly" traveler from anywhere would include a bit of homework on local customs.

Back to the topic at hand, and to the OP - I agree with most others that "sucking up" is definitely not necessary... but if you like the service on the way out, you could always ask if the crew will be the same for the return, and if so pick something up.

Maybe not Starbucks, though - not only would it be difficult to carry, but these days you might be deemed a security risk if you're carrying too many cups of liquid - even if it is purchased on the secure side of screening.