lemme think in terms of my hatchback

passenger seat - 35 lbs
both side panels - 5
rear seat - 20 lbs
headliner - 2 lbs

speakers - 5lbs/ea = 20lbs
motors and lock actuators - 5-20 lbs

any wire, carpet, insulation you can afford to lose could add up quick, also your stereo is at least 7-10 lbs, air conditioner if you got it could be 25 lbs.

air bags could be a bit of weight if you've got a death wish.

and the infamous spare tire and tools, cardboard cover, maybe 30-40 there.

windshield washer fluid is a great place to start just because of its location in relation to th car, the more weight you can get off the front of the car, the better it will perform.

if its stick shift ive thought about dumping my starter, all electric motors are heavier than hell, anything with a magnet basically, (speakers, electric motors, window actuators, starter, washer motor)