This isn't a comprehensive list, but wanted to add a few things:
Turning off the A/C is good, but running the A/C is a better choice than rolling down the windows, because of the drag.
Using the stereo and lights have no effect on your gas mileage. Don't try to limit light usage, for safety reasons, too.
Do regular maintenance on your car. Get those oil changes. Do the work you need to have done every 30,000 miles, depending on your car. Change the air filter if needed, when you have an oil change. Ask them to check it. Check your oil levels. Make sure tire pressure isn't too high or too low.
When choosing a route, highways are best, but if you're driving in the city plan main roads, because stop lights create less stop-and-go traffic. It's stop signs that create the stopping that make you lose out on mileage.
Keeping spare gas in the trunk of your car is unsafe, but I'll admit that I've done it. I kept about a gallon in the safe, approved storage tanks. I'm also an auto club member, and I make sure my cell phone is always charged (or get a car charger), so if I do run out, I'm OK.
I'm cheap and like to drive.