Please don't take the gold coin or the $2 bill. These are basically considered useless tips. No one can spend them. When was the last time you got a $2 bill? Other countries don't want them. They think they are fake. I was in Australia and our bus driver asked me if they were real because someone had given him one as a tip and his bank wouldn't take it. Other countries, like the US, don't want foreign coins so they are unspendable.Wow! I'm glad you replied. I also thought the dollar coin was a neat idea.
Of course the crew member smiles. That's his job. If he sneered at you, you'd be offended and complain and he'd lose his job. So he smiles. Single dollar bills are the way to go every time.
On another note...you gave me an idea for another problem I was trying to resolve. To save suitcase space and avoid having shelves full of trinkets from everywhere I have been, years ago I began buying smashed pennies when I travel. Many destinations do not have penny smashers and I was trying to figure out another idea just as easy. I could just get some foreign currency from wherever I am at to add to my penny box