Just out of interest, are the people who are annoyed by "can I get" all working in retail, serving customers? Because that's the only time you'll hear it with any regularity. Or do you go around earwigging people buying stuff?
Incidentally, I lived in the states for a couple of years in the 80s and "can I get" was one of the few bits of US English that I picked up. I don't think I use it these days. Maybe I do, I'm not sure.