this probably ain't what you were goin for, but as far as music, Bob Marley and Springsteen once shared the same bill at Max's Kansas City in 1973 in New York when both were relatively unkown...would love to have a bootleg of that night.
I would take part in tearing down the berlin wall, and I would soak up the unbelieveble energy all around me. The soundtrack to this would be Albion - Air (palefield mountain remix), or some other inspiring, joyous, energetic track.
I would witness the creation of the universe. It would be just me, and my soulmate (who I have not yet met), having a romantic, intimate experience just watching the incredible view. Of course, we would need a different perception of time, like one present earth second being equivalent to a half million years. The music playing would be the most beautiful, deep sounds to ever reach an ear. It's like how a certain sight makes you feel a particular way, and a sound can do the same. The sound to be heard during this experience has to be just as awe-inspiring as the view.
this thread reminds me of one of my fav SNL skits where abraham lincoln makes a time machine and goes back in time to try and kill john wilkes booth, who then goes crazy and assassinates lincoln cause he looks like the creepy guy in the hat who tried to kill him all through his childhood.
I'd go back to highschool and do it all over again.. not much differently, but just knowing what I know now.. and since i'd already be super smart (by highschool standards) i'd have even more time for socializing