the rear seats dont weigh much at all, removing them wont see much difference. air con is prob about 25kg's worth, lighter wheels would help (mine are like 4kg each :/), removing boot trim, no ice (using ice in the first place is going against what removing weight would achieve :/), if you want decent tuns use a small lightweight amp and some decent comps in some sort of custom pod, will be nice and light and sound good. although, the reason starlets handle like crap in the first place is due to several reasons, the main being they're TOO light, they skip all over the place and dont get as much grip as they would if they were heavier, so being too lightweight aint always the best idea, especially for handling.