I would honestly stay away from ANY mixed drink in a bar. This even includes a rum/Diet Coke. The reason is because in most bars, the shots are not measured. They do a guestimate pouring, so you could end up with an actual shot of liquor, or a double-depending on how much the bartender is paying attention, or how cute he thinks you are.
You want something that you can control more. There is a light beer called Michelob Ultra that is 90 calories a bottle. It isn't the best tasting beer in the world, but it is one of the lowest calorie ones. Many bottled beers are around 12-140 calories each. (Bud Light, Coors Light, etc.)
I have never heard of the Jack Daniels that is 5 calories. I don't understand how it could be, because the alcohol gives it calories...so the higher the proof, the more calories in alcohol it has. So, unless it was nothing more than a diet soda with a drop of Jack, it can't be 5 calories.

(This goes for liquors like rum, vodka, gin, etc.)
If the bar or club you are going to has wine, I would go for a white wine spritzer. Basically, half wine, half carbonated water. A glass of wine is about 100-120 calories on average, so if you made it into a spritzer, it would be about 60, since it is half carbonated water.
Go for that, or the light beer in the bottle-and look up the specific calories for whichever one you are going to drink.