I was told that agave tequila with fresh squeezed lime and a splash of club soda makes a "healthy" margarita. It's called the "NorCal" margarita. It's pretty good. I usually added a splash of 100% (no sugar added) OJ to it as well just for a little more flavor.
Most hard liquor has little sugar, it's all been fermented out. That doesn't mean it doesn't have some calories. Mix that shite with soda or water to keep it as low cal as possible. Try subbing lime flavored sparkling water for tonic. You can get it at whole foods.