All alcohol contains calories, but there are some choices that are better than others. Avoid fancy drinks with high-calorie mixers and stick to more waist-friendly drinks such as a glass of wine, vodka, or light beer.
In terms of hangover prevention, alcohols that are darker in color, such as brandy, whiskey, and tequila, have more congeners, chemicals that have been linked to hangovers. Stick with liquors and drinks that are lighter in color, such as vodka, gin, and light beers.
Caffeine has dehydrating effects, so a highly-caffeinated mixer will only amplify the dehydrating effects of the alcohol, leading to more hangover symptoms. Moreover, caffeine will counteract the alcohol's depressing effects, potentially causing you to drink more. High blood sugar levels can also lead to dehydration. Moreover, sugary drinks mask the taste of alcohol, allowing you to drink more without noticing it, thus increasing the risk of a hangover.