You never know when or where you will be when SHTF. As posted in another thread, you may be 1,000 miles away from your BOL so you need to maximize the fuel economy of what ever vehicle you are in. It doesn't matter if it is a truck, a car, or a van as the same principles apply. So, here is a list of dos and don'ts to get the absolute highest fuel economy possible.
Don't run the a/c. the air conditioner compressor can take up to 7 horsepower to run and that can make a substantial hit on the fuel economy from running it.
Do lower the windows on one side of the vehicle about 1" down from the top in the summer time. By only cracking the front and back windows only on one side it promotes the air to swirl in the vehicle which will make it bareable even in 100 degree weather.
Don't try to modify the vehicle to get better fuel economy, especially if it is a newer vehicle. Most newer vehicles will go into a "limp" mode if any of the emissions devices are modified thus severely limiting your speed and in most cases the computer also forces the motor to use more fuel when this happens.
Do slow down. A typical vehicle will get half the gas mileage of you cruise at 90 mph vs. cruising at 50 mph. Most vehicles get the best fuel economy at about 50 mph.
Don't drive at night. Running the headlights put a bigger load on the alternator which will in turn use more fuel. Not only that, but it is much harder to see road blocks or problems ahead at night. It is also very easy for others to see you well in advance at night vs. the day.
Don't hit the brakes. You need to prepare for a stop as far in advance as possible. Let the vehicle coast to the stop. Hitting the brakes is nothing but a waste of fuel.
Do use gravity to your advantage. Accelerate when going downhill and ease off the gas as you go uphill.
Do go easy on the gas pedal. Sudden changes in throttle input can cause the computer (or carb) to suddenly inject a lot of fuel.
On most vehicles in the winter time you can block off most of the grill opening. This improves aerodynamics and helps to save fuel, but you need to be careful as to not overdo it and cause the engine to overheat.
with doing the above tricks, I have gotten 34 mpg out of my old 2006 Chevy Colorado pickup. With a 19 gallon tank, this would have yielded 646 mile range.