FILL HER UP

Fill up at Arco

Year after year Chevron and Shell are making new record earnings while squeezing the poor motorists for every penny. They advertise their expensive gasoline with buzzwords such as Techron, V-Power and some other BS words. Basically, that means they put some expensive stuff into the gas to sell it at a better profit. In fact, the gasoline of all gas stations flows through the same pipeline and the only difference is the magic stuff they poor into the gas to claim a cleaner burning fuel or better fuel efficiency. At the same time their average gas price is about 10c - 30c above other cheaper gas stations in the neighborhood. I can see no difference in my gas mileage when I empty a tank of Arco vs. a tank full off Techron enhanced souped-up high tech additive gas spritz. And if it cleans anything then certainly my wallet, which is all squeaky clean after filling up.
Well, I am tired of financing the billions of those mega empires. I am getting my gas at the Arco and I have never had any trouble with the quality. Of course you are free to throw your hard earned dollars at Chevron (pay 10% more and save 3% on their rebate cards - another scam to tie the customer to their high priced gas) or Shell in the hopes their magic bullet fuel additives do anything for you.
Now let me back up a second. Sometimes I actually go to Chevron to fill up. I put exactly 8 gallons into my tank so I qualify for a discount at the car wash. 
When I am on the road, I try to keep an eye open for gas prices along the way. If I see the price jumping down, i usually fill up. Some gas stations offer free coffee with fill up or a free hot dog, and if their gas costs the same as the gas across the street, I go for the coffee with my gas.

CLOSE IT UP

Close your windows

 Believe it or not, but opening your windows will increase the turbulences and eventually cost you fuel. If you can, use only the ventilation system of your car. I cannot really gauge this against using the air conditioner. I believe that opening your windows at low speeds and using the air conditioner at high speeds gives you better fuel economy

DRAFTING

Drafting

 Drafting has given me some excellent mileage when I used to commute long distance a long time ago. Obviously, it requires a bit of skill and it's not exactly recommended, since you should pay attention to the road and we all know, most people who read this just don't. However it is probably one of the best "secret" fuel saving tips I can give you.
This technique is frequently used by race car drivers to gain speed and truck convoys to save fuel.
Every car has a certain amount of drag (or wind resistance). This drag, the rolling resistance of your tires and the friction in your engine are the three main causes of reduced efficiency. A car moving through the air causes the air to split around the car and turbulence behind the car. If you drive your car into another cars slipstream, both cars will save fuel (less turbulence). The following car saves the most gasoline.
Now remember, I am not advocating to tailgate. However, you can try to find a large truck (more turbulence and a longer slipstream tail) and slip in there. Now you can still keep some distance (unlike the NASCAR driver) and still save gas.
However, many people cannot regulate their speed without braking (see above). In this case you are probably better off just keeping your distance and not braking.

SLOW DOWN

Drive slower

Yeah right. Obviously thats not something I am all that fond off being the leadfoot driver I am. Well, it's a proven fact that driving fast will increase the drag (turbulence) and thus increase your fuel consumption, however I simply cannot bring myself to drive below the legal speed limit. It's your choice. There is not that much difference between 60mph and 65mph in terms of fuel consumption. However we all can't live in Germany (no speed limits). A car racing along at its maximum speed of 200km/h (depending on the car), would consume about twice as much gas as if it were driven at 160km/h. At the upper end of the power spectrum engines become very inefficient.

SHUT IT OFF

Turn your car off

 When you turn on a car, it uses a bit of gas. When the car is idling, it uses a fixed amount of gas over a period of time (especially with the AC on).
In most scenarios (depending on the car), the energy balance will be positive if you turn off your car for more then 20 seconds.
That means you can save gas if you turn off you car while waiting at long traffic light sequences, railroad crossings or while your better half pulls money from the ATM. Any time you can foresee that you will not be moving for more then 30s or 1minute you should turn off the engine to help your vacation budget.

LOSE THE WEIGHT

Reduce weight

Coming back to the force equals mass times acceleration. We already established that one shouldn't accelerate as much. You can also try to reduce the mass of your car by emptying out the trunk and removing heavy items that you don't need (keep your spare tire and car lift, but get rid of the gardening equipment).

AUTOMATIC

Shifting Automatic

If you have a cruise control and there isn't a whole lot of traffic, you probably should use it (it will keep the speed constant and hence doesn't need to accelerate). Use the overdrive gears, as this will generally keep your RPM down and your wallet happy.
 Shift into neutral when you are standing still to reduce transmission strain and cool off the transmission.