I use iTunes to manage music on my Mac, not just because it supports my iPhone and iPad, but also because both Sony and Microsoft provide tools for syncing music between iTunes and their phones. Makes things nice and neat and allows me to manage the music I own in one place.
If I want to send music to a USB drive things aren't so simple however. The tradional way of doing it is to drag the files from the iTunes windows to the USB stick where they will be deposited with no useful ordering or playlists.
Enter iSyncer, a free, donation supported tool which allows you to sync from iTunes to a USB key without losing any of your precious efforts in creating playlists.
Other than a requirement to have JRE installed there's nothing much to do. Fire up the app, select your USB drive, playlist format and the playlists / music you want to sync and hit go. One very short wait later you have a flash drive with your music transferred.
A relatively simple tool to accomplish what would otherwise be a less than simple task, it's available for both Windows and Mac, from this website.