FolderSync - Sync Playlists or the whole Library with a folder! You can use USB-Mass-Storage-Devices with this Add-On. If you use Rockbox on a FolderSynced device, you can also track your play counts.
FolderSync gives you the opportunity to sync songs to any folder you can specify with an absolute path. So you can for example sync with USB-Mass-Storage-Devices.