So many there's a lengthy list on Wikipedia about it. It's fascinating reading ancients casually referencing works that we otherwise know nothing else about. Without the careful, laborious copying (often imperfect) over the centuries most things would've been lost completely. There's also other works such as maps that did not survive, the Tabula Peutingeriana for example is thought to be a derivative work of one commissioned by Augustus of the known world at the time (to Romans) and of which there's a few mentions in some works by historians at the time.
This is the most exciting thing in the world to me right now, these scrolls, along with the thought that there might be literally thousands more still in the ground.