Start with the basics really... Its been stated on these forums before that just acquire some dry ice and pour it on the sound deadener, should peel off. Seats of course can come out but depending on your state you may need to get it engineered for the rears removed or you cant altogether!

Replace front ones with carbon-kevlar units, if you wish to go to extremees then get some carbon fibre or FPR panels made, lightweight suspension components, titanium exhausts, stripped interior, lighter flywheel, using lexan/perspex for windows.

Thats going to extremes though