Originally Posted by cwilliamsws6
And I got the car with 193,000 miles 3 years ago, so 210k-193 / 3 , equals to about 5,600 per year.
As others already mentioned, your biggest potential for MPG improvement is to adjust your driving patterns, and remove any extra weight from the vehicle. The fact that you're running a power hungry sound system probably doesn't help MPG either.
As far as additives go, even if you did find some miracle concoction that could MAYBE improve your fuel economy by 2%, we are talking roughly $15-$20 in total annual fuel cost savings, given your annual mileage. Hardly worth the trouble, IMO, considering what it would cost you to purchase said concoction.