You dont have to start by stripping interior although most people do. Use lighter weight wheels to reduce rotating mass, lightened flywheels, aluminum pulleys, aluminum driveshafts, removing a/c, power steering, and removing the heavy steel or iron brackets that hold these items on. Use fiberglass/cf hoods. Use lexan instead of glass for the rear hatch. Remove sound deadener underneath interior. Remove spare tire and jack if you feel lucky. For those not concerned with safety like myself… removing bumper supports takes out over 50 lbs in some cars. You could easily pull out 200 lbs+ without even touching the interior.