Wine and champagne
It should come as no surprise that a good bottle of wine or champagne has its cost multiply as it moves from the vineyard to your table.
According to the magazine Wine Spectator, an average restaurant can be expected to charge double what it paid for a bottle.
An in-demand bottle can even fetch a 400% markup sold by the glass.
Liquor sales have always been a money-maker for restaurants, boosting their bottom line in a way low-margin entrees can't always do on their own. High-end alcohol sales also carry a prestige factor that, in the eyes of many diners, makes up for what they are shelling out.
The markup will get you even if you BYOB. Restaurants allowing you to bring your own bottle will routinely tag on a $10 to $25 "corkage" fee.