I always thought the mark up that places made on on food and drink, went to pay staff wages etc.. having to tip to get proper service really irks me
It should be a REWARD. NOT a requirement.
I think USA bods have an 'expectation' of 15-20% of goods purchased.. For porters etc, though, no idea. Depends if you have a small case, or a huge chest (fnar..)
Pay whatever you feel comfortable with, and to whoever think deserves it.