Debbie, I have heard that about using the AC vs keeping the windows open. I am not sure what is more gas consumptive - using the AC or having a lot of drag in the car from open windows.
There are sources arguing both positions: when to use the AC or have open windows in a car
One site on hybrid vehicles poses these responses: "If you�re driving around town, or in city traffic, then you�re better off leaving your windows open. For highway driving, roll the windows up and turn the air conditioning on. It�s advisable to roll the windows down for city driving, because speeds lower than 30 - 40 mph vehicles consume less fuel, then using the A/C at those speeds. Using the A/C at highway speed has no appreciable effect on fuel economy compared to rolling down the windows." -- go-hybrid.info/air-conditioning.htm
Most sources agree that for errands, in-town and city driving, open windows are the better answer. For highway speeds and long drives, flipping the AC switch is best.
I would posit that keeping the car as cool as possible when parked is at least a great place to start! And doing errands at night!