seats are a good place to start, they weigh like 50lbs or so, especially if you had power seats, you can get some decent racing seats that weight a hell of a lot less, I know the hatch lid weighs a lot, if you were to somehow cut off the excess metal. The door have a lot of excess, you could trim the door panels.

if youre looking to take some off the engine, the crank pulley, get some lighter performance pulleys, you can do it yourself with the help of a friend pretty easily., every lb off the crankshaft gives a small hp boost

 

Aside from whole interior removal, there isn't much. If you have a TT, removal of the HICAS system saves some weight. Removing of the stock seats will save you some weight as well. Power seats because of design are inherently heavy. Some racing seats would be a suitable replacement. I've seen some go as far as replacing the rear hatch with a fiberglass and lexan replacement. Fender replacement with carbon fiber or fiberglass components might lighten the load there as well.
Then there's the drivetrain lightening that could be done. Valves and springs in the heads, lighter engine pulleys, lighter flywheel and lighter driveshaft all contribute.

 

throw your spare out. and use just one seat

 

Don't put a lot of gas in your car...if this is for the track that is. Have a seperate tank of race gas with you.

 

It really depends on how far into you want to go. You can get rid of the AC, cruise control, power steering, door panels, dash, stereo, all interior paneling. Take out what you don't use and/or what you don't care about having.