I'd invest in some lightweight plastic seats if you are that seriously into weight loss. I have a pair that I had in mine for a few days, but I drive my car ALOT and couldn't put up with them every day. its atleast a 40-50lb savings right there.
Harwood sells lexan windsheilds for about $90, something else to think about.
The stuff behind the dash isn't too heavy, but every little bit counts, so go rip it outta there!
(i gotta do that this winter)