Best way to use guarana, or any caffeine for that matter, is right before your workout. I always have a coffee before I go to the gym - it help a lot.
My vote for alcohol is white wine. Besides the fact that it is delicious, its reasonably low in carbs, and you don't need to drink too much of it to get an effect. And probably a bit heathier than the diet soft drinks that you'd have with spirits, jsut cos of the artificial sweetners etc. (Aside: just learnt something funny about soft drinks - did you know the main ingredient is phosphoric acid, which is... horse piss!!! Its true
Turned me off soft drinks for good now I think