Guess this one is a little old.
I think everyone has had great ideas so far. Considering myself as somewhat of a car nut a big thing that sticks out to me.
Easy answer drive like you have an egg under your gas pedal. Coast to stop lights etc...
Air up your tires. Changing you own oil depends. Shops buy bulk and can compare to your cost if you buy name brand or better oil. But if you have a good oil, you can get up to 10,000 miles before you need to change it. (hit 20k on my 03 Chevy last change)
In this world, something I have done (started in Aug, so I have not saved a penny yet) is to plant 2 Apple, 2 Pear, 2 Cherry, and 1 Nectarine trees. All in all about 160 dollars or so. But the first year I get a good fruiting off them, they will be paid off.
I also have 7 Blueberry bushes, 2 Raspberry bushes, and 2 Blackberries.
Huge pile of seeds to plant. Alot from the Coop from last year. 50% off at the most. Got 3 pounds off bean seed and one small packet of Okra (about the same as 5 or so of the paper packets of seed) for $5.05. Loving the Coop as it's about 5 miles away.
I have a composter, going to add a second. This is a time to cost thing to me. I spent 130/140 something like that. So it's going to take time to pay itself off, but in time it will. Have to figure the better your garden does the quicker it pays off, the quicker you can make compost the quicker it pays off.
Speaking of cars and such. If you "need" a truck but only in the summer. An S10 or Ranger that gets better mileage but can pull a small trailer when the "truck" is needed can save alot of gas. A good trailer will cost some, but even small trailers can be had with a 3500 pound axle. My newest trailer has a payload of 2,900 pounds. More then I can put in the bed of my 03 3/4 diesel Chevy on an average day. Bad thing is tires need to be replaced every few years. (every 4 to 7, they just get old)
Depending on your level of expertise. A Haynes or Chiltons manual is great for general car repairs. Problem is buying tools if you do not have them is not cheap. But most car repairs don't invole alot of "special" tools. Plenty of forums like this to help if you need it.
Dig through your house and see what you can either have a garage sale or put on craigslist. I take my trash to a "dump" site every week. Save more spending the gas money they paying the city. I also grab some stuff now and then. Found a vanity that was a little old and beat up. Glued a drawer back together and sold it for $40 the next day.
I save any and all scrap metal. Have a scrap yard about 8 miles from my house. Saving all my cans too.
I have also used 2 liter bottles and milk jugs to start plants in.
An older car even with repairs can be cheaper then new. Insurance is cheaper, car payment is nothing.
A flower garden in the front yard, back yard, or both can cut down on mowing and save gas. Also something like a railroad tie level with the ground can be mowed over and save on weedeating.
A wood grill can save money, free wood on craigslist alot, just have to pickup and cut.