My '07 Aveo is:
5 sp manual
no special enhancements
142K miles

I can average 37 MPG on the highway, and 32 MPG city driving.

I'm in the process of cleaning the car up, and replacing/updating all the obvious maintenance issues with the car.

I used to be able to get 46 to 50 MPG on I-71 in Ohio, on the Cleveland to Cinci jaunt, that I used to regularly make.
I adhered to some "hyper-miling" tricks that I had read about.

I kept the windows rolled up, usually no climate control usage, just the air coming through the vents.
I had kept my tires inflated to 35 psi, a tad higher than recommended.
I did the speed limit posted, and would obviously use the hills on I-71 to my advantage.

Now, keep in mind, I NEVER shut off the car and coasted down hills, the way some people who hyper-mile claim they do. I do not trust that there will be no engine damage trying to restart a car while rolling at 60 miles-per-hour.

I also, very rarely, would draft off of trucks.
I was always concerned, since I grew up in the day of land barges, and my first car was a 1977 Oldsmobile Regency 98, that such a little car as my Aveo might get blown off the highway if hit with too hard a wind sheer.