if you don't mind a really noisy car you can take out all the sound deadening material. that stuff weighs heaps. but good luck selling a bmw with no deadening material in it.
saving weight is really only worth while if you are plannin on taking out LOTS of weight and by that i mean stripping the interior, carbon fibre body panels, getting rid of the unnecessary compononts like ac, power steering, stereo, etc. otherwise its just pointless