Regarding gratuity, if you order a drink at a bar in the United States, etiquette dictates that you should tip the bartender at least $1. The bartender is already paid to be there, though usually less than minimum wage. For a task that may be as simple as popping the cap off of a bottle of beer, or pouring liquid into a cup, we as a society have decided that they deserve an extra dollar, and hand it over without much thought.
Meanwhile, musicians are scrounging for tiny fractions of pennies.
I used to write notes on the dollar bills I'd leave as tips at diners and bars. Little messages to the world. If one made it back to me after twenty years in circulation, I wonder if I'd even recognize it?