Be careful that when you order a "call drink," ie., a drink by brand name like 'Grants' or 'Johnny Walker Black' that it really is Grants or JWB they are poring into your glass.
The tourist authorities don't want you to know this, but there is a big black market in "Bomba" alcohol being served to tourists Greek and non alike, particularly in the summer in hot spots like Santorini and Mykonos.
Bomba won't kill you–you'll just go blind (only kidding?). Is this part of living your myth in Greece? Likely after the first couple of drinks you can't tell the difference anyway. I know this because an acquaintance of mine confessed to me that he used to own a bar on Santorini and would serve 'Bomba' to his clients when he could get away with it.
Another Greek friend is so afraid of Bomba he goes the other way and only orders locally produced and commonplace liqueurs like Tsipouro, Raki and Ouzo. Thinking about it some, I bet that Tequila is a drink difficult to counterfeit and ordering one probably safe. A shot of any the above three is about as strong as a shot of Cuervo Gold tequila. That's pretty strong. Mezes or appetizers are a common excuse to visit tsipouradika or ouzeries specializing in this kind of repast. A tapas bar comes to mind with out the bar. An Ouzo hangover is one of the worst you can have - drink water too.
Most restaurants and bars geared towards the unwary do not have barrel wine. Santorini is famous for its wine and a place where the barrel wine is amazing. Santorini bottled wine, in a store, is inexpensive and excellent too. But why pay extra in a restaurant for the same bottled wine that you can get out of a barrel for less? Santorini has the right climate and soil for wine grapes. It's hot in the day and the soil is volcanic. At night the humidity works in its favor too! The island grows over 36 kinds of grapes for wine production and in late August it's harvest time. Tours of the wineries are available. Stop by these wineries for free wine tasting.
September at the yearly Daphne Wine Festival in Athens you can taste all the wines of Greece for a small admission fee. See the Athens Guide for more info.