It depends on where I am, the time of day and what I am eating. I almost always get an unsweetened iced tea, for the caffeine, and then usually order at least one glass of wine or a cocktail. If I am out with others I tend to follow their lead because I don't want my drinking to make anyone uncomfortable. Sometimes, if I want to save money, I just order the iced tea because the mark up on alcohol in restaurants is outrageous.
I don't drink any alcohol, so I usually drink soda instead. Or water. Or juice. That's the only beverage that resto's tend to offer anyway, so if ever one will treat me to a rest,o then he/she will save money on buying alcohol because I don't drink at all.
I usually just get water, but if I'm craving for something sweet, I'd order a fruit shake or fruit juice or occasionally even a soda. My favorite thing to order is really fruit shakes, though, especially watermelon which is my favorite, partly because even though I know they are packed with sugar, I at least can rest easy that it's surely still much healthier than a soda since it at least has fruit. Also, I much prefer just ordering this at the end of the meal so I can have it as a dessert because I don't really like the thick texture of it when it comes to pairing it with food.
I hate ordering alcoholic drinks at restaurants because the markup on them is so high, and they are typically poured super weak in tiny glasses. They're like $6 a piece, and I only get a few sips out of them. The only time I will order them is if I am waiting at the bar to be seated, or waiting on some other people to show up. Other than that, I may have an alcoholic drink at the end of my meal, in lieu of a desert. Something like a Negroi, or maybe some Grand Marnier warmed in a snifter. It drives me nuts though to ring up a $40 tab on drinks at a restaurant, when I could have bought a whole bottle of something for less than half that, and had many more drinks.