Nothing fancy, though a car shaped like a barn isn't necessarily the best place to start when looking for efficiency.
Current Mods:
Moon discs, if they count. I bought them for the look, admittedly. Turned the cold air intake into a warm air intake. Tires @ 45ish-psi. Grille 85% blocked. Coroplast undertray behind the front bumper. Gasket under the leading edge of the hood. Lowered ~1".
Still refining the performance of the nut behind the wheel...
Planned Mods:
Scangauge, air dam / belly pan, better driving. Maybe lighter wheels?