Yeah, it's a little secret thing in my sig...
Ken_g6 got it right.

You guys are actually the first people to notice it and say anything.
I don't think the juice has any specific flavor. I just remember it being called "multivitamin juice." Like orange juice.
As for the packaging, the stuff I bought in Munich came in a clear one liter glass bottle. I think it had a white label on it, but I can't remember for sure.
I was doing some looking last night, and it seems that Tropicana Europe makes some multivitamin juice under the Looza brand name. However, the bottles look different than what I had, so I'm not sure if it's the same stuff.
BTW, from what I remember the multivitamin juice is pretty common all over Germany (southern atleast). Besides buying it at the Munich train station I remember buying some at a grocery store in Garmisch.