anyone know? like seats, and stuff

 

Search for "weight reduction".

 

not very much. ~40lbs for all of the sound deadening tar from the firewall back to the trunk area, ~25lbs for door panels and all other plastic panels, ~10lbs for the rear seat, ~5lbs for the rear speakers, ~5lbs for the carpet...

There's lots more than you can do, but you're starting to kind of destroy the car at that point.

 

It just doesn't seem like it's worth pulling the back seats and trunk carpet out of Hondas. I doubt 10 lbs. is going to make your car go that much faster.