There's also no need to accelerate to 20 mph in first gear like a maniac when you need to stop in a few meters, thus converting all the energy in the movement you just built up to heat in your brakes.
On the highway the drag does matter.
Also keep in mind that the AC uses fuel per the hour, not per distance. So in the city when you're going relatively slow the AC will affect the MPG much more (and city MPG is already terribly low).
Get a white car and it will heat up less, so your AC will use less fuel.