Hmmm...
1) Mozart - because he composed so much, it would take a long time to finish listening to them all. And it encompasses all (or nearly all) of the genres in the Classical period. I would die without his operas! Is there a DVD player onboard?
2) Bellini - for sheer beauty and elegance of bel canto writing.
3) Bach - despite not being one of my favourite composers. Something substantial to keep my brain occupied listening to and analysing his counterpoint techniques.
4) A compendium of the most significant early music works. So maybe including Tallis, Byrd, Gabrieli, etc. I've recently taken an interest in early music - me thinks thanks to MissLimLam, Hafwen, and my music history professor. You guys (girls, actually) are gradually turning me into an early music nut.
5) Puccini or Verdi...I can't choose! Maybe Puccini. But I want Otello, Rigoletto and Traviata too. Oh well, Puccini is more different from Bellini's bel canto style, so I think I'll go with him. Final answer - Puccini.
If I'm not allowed to go with my #4, I'd substitute it with Beethoven.