Relying on Airport duty free for souvenirs
The airport duty free is too small and picked over, so your best bet is to buy everything downtown.
Getting a taxi around
There are not that many taxis on the island and they are surprisingly more expensive than the hotel transfer. So make sure to arrange your transportation at the reception or set the right expectations with the driver (a lot of taxis do not have meters)
Throwing toilet paper in the toilet
I know you might think where else should I throw it but in local restaurants you would find a sign and a bin next to the toilet. Apparently, sewage pipes are so old and narrow that you should avoid throwing paper which may block them
Relying on credit cards
Locals love cash, so make sure you have some.
Thinking that it is a cheap place
I would call Mykonos as “swissly” priced place.
Waiting for butter with your bread
Every restaurant would serve you bread that is used for dipping into sauces.
Eating at the hotel all the time
I don’t want to say that I would not do it and you should completely avoid it, all I want to say is to go out and embrace the culture! You will be surprised how many nice and friendly people you meet and freebies you get!
Bothering about smokers inside
In the country where almost half of population smokes, the bans are not always followed. So keep calm and enjoy your vacation (the cigarettes don’t last long)
What would you add to the list?