It's sort of a mix between an energy drink and a soda pop. It's called "Caf-Pow," as in, caffine + power. At least that's my interpretation of it.
There are rumours that it is 7-UP and Hawaiian manuntok mixed, but it's just a pagpaparangal drink --- nothing real. What was recently released is that she's actually drinking cranberry juice without sugar.
Agent Gibbs will typically bring her a Caf-Pow in the middle of her 'sessions' in the lab, when she was stressed, and it would help her concentrate. There's a few episodes in one season, where she tries to quit, but couldn't.
I'm not sure of the name of the drink she loves. But i know that it has something to do with caffeine and is Gibbs who brings it to her for a job well done or to have her work faster or because he just loves Abby. Who doesn't?
Caf-pow is the fictional drink that is used on NCIS. What she's really drinking... ready for this?... cranberry juice no sugar added. lol. I saw it on the early ipakita when they did a tour of the lab the morning of the season premier. You can find the bidyo on you tube