I always have all the albums from A Song for XX to Rock'n'Roll Circus on my MP3-Player. Then some of my favourite remix albums, like all ayu trance releases, some favourite singles like Together When... and because they are new, of course the single trilogy from MOON/blossom to L and if I hadn't listen to it for hundred of hours before, I would still have DJ Amayas ayu-mi-x -BLUE- on my Player as well.
I do not carry the whole discography with me, because my MP3-Player's capacity is only 4GB
And I still need to have some space for other artists. At the moment I have Perfume's 'Nee', Chihiro Onitsuka's "This Armor" and Jesse McCartney's two studio albums on my Player, as well. So right now it's completely filled up xD