Something you can consider with the car is the ability to lose weight on a larger (smaller?) scale.
Just because the rear seat weighs 50 lbs doesn't make it the most useless weight in the car. Often, there are areas that are braced and don't really need to be, like the rear hatch. Behind the plastic, you can cut some 1" holes through the upper brace where the hatch bolts on. It's only a few ounces per hole, but they add up. If you're serious about losing weight, it's only going to take a few thoughts and a good plan.
In fact, I've actually replaced floor pans with aluminum plate, replaced seats with lighter OEM versions, replaced OEM parts for lighter ones (usually made from scratch, like the front cross member on 4th gen Civic/ 2nd Gen CRX models.) etc. There is LOTS of weight to be lost.
If you don't ever find yourself looking out/needing those 1/4 windows in the back, remove them and replace them with body-type sheet metal or aluminum panels. If you do happen to use them, replace them with lexan. It's lighter than glass, and still legal in most states if it's not a "primary window". (Driver and passenger door, front glass.)