Yes.
If you want to save the whole library, copy the entire iTunes folder to the drive. (Note 1. First make sure the drive has room, since many libraries are bigger than many flash drives. Note 2. If your library is not already consolidated, run Consolidate first, as this will assure that all content and all library data is together in the iTunes folder.)
To copy a playlist, highlight all the tracks in the playlist, and then drag from the iTunes window to the flash drive window.