Great stuff from Home depot can be used in many good applicagtions, although it doesn't look very good in the trunk, it can be used as GREAT insulation and a big gap filler.

next is pink insulation, again not very good and also most for sound and you dif want to hide that stuff in the box if you can. It can be painful and messy

another is Egg cartons, This can be while. Or carboard like in the shape of egg cartons. Not your best bet and hard to work with.

Other then that you can go for Dynamat and spend oh..about 100$ for a 1X1 square sheet and support the money staving bastard. (sorry I am not impressed with dynamat's price) or use 3rd party stuff like it.
check around on the internet like that guy above posted (b-quite)

Fiberglass can be useful but it's also a whole new story and again time consuming.

OR out of it all, just turn down the volume and don't listen to loud angry music???

 

Oh!! I also forgot too.

There is also another messy option and that's Rubberized undercoating gaurd spray/can.
I used some of this stuff in a civic once and it worked perfect.


Check this site out might give SOME help? http://sounddeadenershowdown.com/