Teach you one instant recipe to power. Throw away your spare tyre and any other unused items! Then you already tweak the weight part of the performance equation. It's free and it works.
QFT. Get rid of junk and rubbish inside your car. Then, invest in lighter rims, body parts, seats, etc2....easiest way to improve power-to-weight and FC in one go. A diet also helps...hehe