The Gemini is a FTL-capable freighter in the fleet which Valerii escorts to the convoy after the cylon attack.
Upon its arrival, Valerii and the Gemini are greeted with the words, "welcome back, Boomer. Got a lot of thirsty ships here eager to make your friend's acquaintance." From this, one might be lead to believe that the Gemini was transporting water or fuel. (Mini-Series)
The Gemini also features in the original series. This is the ship that Cassiopeia is rescued from (Saga of a Star World (TOS)).