I've set up several playlists on a USB stick and (If I'm doing it correctly!) they're a PITA actually, if I switch my car off whilst listening, next time I switch on, the head unit will play the first song (alphabetically) in the first folder in the 'music' folder.... There's only a certain amount of times I can listen to Adele

... Then I have to browse to the bl00dy playlists again and find the one I was previously listening to....
I've since just made new folders and named them something like 'Various rock'... 'Various smooth'....'Various etc etc....and just dragged the songs/tunes into the folders, they probably appear in their respective 'album' folder as well, but with a 32G USB stick there's plenty of room there!
Every now n then I'll plug the stick into my PC and update/renew the 'Various.....' folders much the same as I'd update the playlists....
Simples