I avoid the mays and cans by saying "I'd like a ... please". Or maybe "Could I have a ...?" I'm more concerned about being understood than the grammar being correct.
Similarly, since I understand what the response "good" means when I ask how someone is, it doesn't bother me in the least. Language is for communicating. If it does the job, why by picky? I think clarity of speech and articulation (same thing?) are more important than a person's particular choice of diction, which latter is probably driven by whatever is fashionable in their social milieu anyway.