Truck stuff, spare tire, jack, carpet etc. A/C all the lines, compressor, condensor, fans, evap, etc, maybe the heater to?. Replace front seats with lighter one but this will cost a lil money. Basically whatever you can live with out. You could take out seat belts and replace them with aftermarket racing harnesses for the front. Remove the air bags and the rear and front crach beams but i would only remove the rear and leave them if you are more concerned with safety.
i have the japanees engine the dual cam ZC non vtec with a tdo4 wrx turbo with a skunk2 intake manafold chipped ecu, aem fuel rail and pressure regulator, aem cam gears and greddy bolt on exhaust but i want it faster!!!
this is why its good to have a HF crx already light then take out everthing but the seats and it gets even lighter i hade a 4 door there really is no point in it till you have almost a fully bolt on motor or built motor befor you do it i wouldnt waste the time and energy in it