You're right. What you're describing is what engineers are indoctrinated in, called Lean Six Sigma. "L6S" can be summed up as "large improvements can be gained trough the sum of many small improvements."
American Airlines went on an L6S kick years ago. They saved millions of gallons of jet fuel by not painting most of the outside surfaces of their planes, threw away most of the magazines in the cabin, just carrying enough beverages to get them to the next stop, only carrying enough fuel to get to the next stop with a reasonable margin of safety, etc., etc.
I actually shut the car down and roll the windows down when I'm waiting for Frau Putzer to bring me my hot chocolate and tasty breakfast sammich. Frau Putzer, on the other hand, has no problem sitting in a car with the engine and AC running. I haven't done an idle-fuel-consumption measurement on her X3, but since it's a two-liter (compared to my three-liter), it probably burns about 0.25 gallons/hour with the AC running. We met for lunch Tuesday, and she got there a few minutes before I did. There she was sitting in her car/truck with the motor and AC running.
Our BMW's need 91 AKI gas, but they don't sell it here. So, I make my own by blending 1/3 87 AKI and 2/3's 93 AKI. That saves $3 to $4 per tank, and about $800 over the 100k miles we keep our cars. It takes me an extra minute to do that, but that works out to $120 to $160/hour for my time.
I don't use the recommended tire pressures on the door jamb decals. Instead, I measure the tread depths (each circumferential channel on each tire) when I rotate the tires
and adjust the tire pressures for even wear. That almost always means higher pressure than what the decal said. My tires
last longer (because they wear evenly), and I get better MPG. I give up some ride quality, though. My top five mileages for a set of tires
are: 79k, 74k, 70k, 70k, and 68k miles. The 74k mile tires
were on a 1/2 pick-up truck. I'll get ~55k miles out of the OE non-run-flats on Frau Putzer's X3. That means I'll only have to buy one set of tires
to get to 100k miles.
If I see a line of cars ahead stopped at a red light, I throw my manual transmissions in neutral and start coasting up to them. Later BMW's (starting in 2014) actually build this logic into EcoPro Mode in cars with automatic transmissions. Planning my stops and using engine braking when possible and necessary, my first BMW still had about 1/3 of the front brake pad material left at 115k miles when I sold it.
Actually, BMW's brought back both spare tires
and non-RFT's. You can get a spare tire on every platform BMW makes, except for the F2X 2 Series, F3X 4 Series, and the Z4. The F2X and F3X platforms are old and are nearing the end of their production cycle. Their replacement platforms will likely offer spare tires
BMW's' spare tire rims are now aluminum to save weight. In addition to improving MPG, they're a lot easier to hump in and out of the trunk, and on and off the car when you have a flat tire. At $150, the optional spare tire is the biggest bargain on a BMW option list. On some models, the spare is free if you spec' the optional non-run-flat tires
are about four pounds heavier than a comparable non-run-flat. They also have higher rolling resistance, which reduces MPG by about 1%.
Years ago, I had a rental F-150 with a V8. On a 40 mile road trip I achieved 24 MPG. But, on the same road trip in Frau Putzer's 2018 X3 in EcoPro, I can hit 38 MPG if the traffic lights and wind are in my favor.
One thing that really cuts into MPG is sitting at stoplights with the engine running. But, I always disable the Auto Start/Stop (ASS). Yeah, ASS saves gas. But it also puts extra wear on the engine, starter, and turbocharger. Since we keep our cars 100k miles, I don't want to risk having to replace those components.
Frau Putzer once found a $100 bill on the ground. She damn well sure did pick it up. But, then she said "Look ever' body, I found $100!" I told her to STFU, in case the person who lost it was still around.
A friend if mine found a bail of marijuana floating in the water when he was surfing. He lugged it back to the frat' house and dried it out. Him and his frat' buddies smoked half of it and sold the other half.