nope. regular gas is what you should be using.

Most of the "mods" for better mpg are about picking specific things. Like tires in compounds and sizes. Wheels that are light weight and (controversially) offer little wind resistance. Having good oil, changed regularly. Taking care of the transmission. Lightening the car. Converting to electric and such.

Truly gaining mpg requires technique as well, Driving at appropriate speeds in certain gears. Warming up the car as fast as possible. Not running power draining accessories. Keeping windows up.