I recall some militart freepers telling about going into restaurants in uniform and having people buying drinks and dessert, etc for them... to the point after awhile they had to politely say know.
When I'm in an airport I have some $5s with me and if I see a GI I'll tell him get coffee or whateve on me...
I was at a restaurant in Florida a few weeks ago. To Air Force guys were eating. I told the waitress that I wanted their bill. She ignored me and gave the bill to the airmen. I didn't want to embarrass them so I let it slide.