I consider the manner in which he paid for his drink--and plane ticket--much more compelling than what he ordered. More to the point, we know he paid with a $20 bill for the plane ticket. We also know that he paid for his drink with a $20 bill. We also know that he didn't have anything smaller than a twenty because Flo asked him if he did.
So why is this important?
It tells me that he did not visit a restaurant or sundry shop before the flight that day. After all, if he had he would have been left with change which he apparently didn't have. Of course, one could argue that he used a credit card, but that seems unlikely for a small purchase when he has cash on-hand and that it leaves a paper trail.
Now when you factor in that he had a pack of Sky Chef matches, I believe that we can deduce that he did not acquire them at the Sky Chef restaurant at PDX. After all, he didn't eat at the restaurant as noted above, and it seems unlikely that he would simply grab a pack of matches when he didn't need them--remember, he was using matches with a white cover that he eventually depleted.
All of this leads me to deduce that he flew through or from a city with a Sky Chef restaurant. I favor JFK as I've noted previously.
Now, it is possible that he acquired the matches from a meal on a previous flight. But that, too, suggests a flight long enough to have served a meal--again the East Coast seems likely.
All of this is reasonable to deduce from how he paid for his drink and not so much what he drank--which I believe he ordered as a "bourbon and 7-Up."