Here's just about everything I've done to my car:
Firefly efficiency mods - MetroMPG.com
But the biggest single improvement to my fuel economy has been driving style. And specifically slowing down for highway driving. I averaged 75 km/h driving from Ontario to Nova Scotia recently (with the car fully loaded), and
with some good tailwinds averaged 75 mpg (US). The aero mods definitely help, but #1 is leaving earlier & driving slower, where traffic permits.
Don't forget partial grille block and block heater will really help in the winter - especially out there on the chilly prairies. (How cold has it gotten so far? :P)