"Can I get..?'' when ordering food/drink
I think that is a regional speech pattern. It is absolutely standard where I live, I've never really heard anyone say anything other than that. And whilst I don't know for certain what the history of that particular phrase might be, or if it applies in this case, I do know that Scottish and Irish speech patterns that are scorned as incorrect are actually often very logical when you factor in that the language in those areas have been influenced by other distinct local languages.
I wonder if that might apply in this case?