There is plenty to lose from a car, but that will depend on how far you wish to go. I did the lightening regime on bikes, as I worked on building 750 superbikes, the things you do!
As for cars, well on my track cars the door skins would come off, polycarbonate windows, dash removed and custom one made. Wiring stripped and re-wired for essential items. 2" holes drilled where it isn't structural, these days it means practically nowhere! The usual removal of everything inside the cab.
On my last track day, 19th March, my brother-in-law came along for the ride, so I would suggest just one seat! The extra 75kg really made a difference with both handling and performance!
I'm trying my hardest not to strip mine out as it is a daily commuter, 350 miles a week!