The thing with getting a mixed drink is you don't know how the bartender is "making them". Meaning, a shot of vodka or rum may be so many calories...but in some bars/clubs you may get a drink that is weak...and in another it is so strong that it is pretty much a glass of booze with a "shot" of soda pop in it.
You know what I mean.
A shot of rum or vodka with a diet soda is a good choice-but only if you can see how much they put in the glass. (When a bartender pours a shot-a 1 oz. shot can be poured in approx. a "count of 4"-I went to bartending classes in my early twenties.
If you are out at a concert-you might do best with a light beer or two in a can or bottle-because you can simply "know" that the calories are correct. Michelob Ultra is I think 90 calories a bottle if they have that. There are also a few other bottled drinks as well that are "light" that you can find the info on.
Wine is always good-and it is easier to look at the cup and guestimate "is this 4 oz/half a cup) than it is to guess how much liquor they put in your diet soda. You could end up with 2-3 shots in there instead of one, if the bartender doesn't really "care". (Or thinks you're cute.