Re: the soft-drink thing - I always feel weird tipping for a Coke. I also feel weird *not* tipping for a Coke. A $1 tip exceeds the value of the Coke, but then again, a tip is supposed to be for the service, right?
I feel like bartenders don't expect a tip for a soft drink (I know I didn't when I bartended), so I generally feel OK not tipping for those. But if I have, like, five Cokes over an extended layover, and the bartender was friendly vs. perfunctory, I will leave them a five-spot at the end before I leave. Illogical? Maybe.