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Car engineers spend a lot of time engineering pounds, ounces and grams out of today’s cars. Don’t undo their efforts (and the gas savings they represent) by leaving anything unnecessary in the luggage compartment. Golf clubs are a common violator, but so is random dead weight like those items slated to go to the second-hand store one of these days. Or, dear lord, a case of individual water bottles for after-workout hydration.

Every time you accelerate, you’re using gas to get that stuff up to speed with you. How much more? This depends on your car, but the EPA estimates a 1% reduction per 100 pounds. On a per-gallon cost basis, that’s about $0.03, using the EPA baseline figures. Get your stuff in order and you’ll save money, too.

When they’re not worrying about the weight of their designs, auto engineers fuss over aerodynamics. Improvements to how your car cuts through the air bear fruit most at high speeds — highway miles. The most common way drivers hurt their aerodynamics, and thus mileage, is by putting items on the roof.

Do you have activities that mandate a lot of equipment? Consider whether you could use a hitch-mounted rack or box instead. Tucked in the slipstream of your car, these have a much smaller mileage penalty. And, finally, if your vehicle came with a factory roof rack that you never use, see if you can remove the crossbars. You’ll save a few pounds this way, too.

Being told to group your errands sounds a bit like a nag, much like the admonition not to use the trunk as a storage locker. Still, we will repeat the reasons why planning ahead can save gas:

If grouping trips means fewer miles driven, well, that’s obvious.

Americans continue to wildly overestimate how much fuel it takes to start an engine versus to keep it running. The reality is, once you’re stopped, your car is wasting fuel after about 7-10 seconds of idling. That’s why newer cars have a feature that shuts the engine off during stops when the brake is applied. The car’s still on, but the engine isn’t. Push the accelerator pedal and the engine snaps back on — off you go. Some people find this maddening, but the gas savings is real. If you want to maximize mileage, don’t disable the auto on-off feature.

Finding the cheapest fuel was once sport for me. But phone apps like GasBuddy, Gas Guru and Fuelzee make it almost too easy to find the best gas deals. Since you can use them to screen for brands, you can also make sure you’re getting good quality fuel, which, in the long run, matters to the health of your car.

Joining a membership club like Costco or Sam’s Club could also pay off. Figuring how quickly you’ll recoup your membership cost with the per-gallon savings on their discounted fuel is pretty easy math.

All cars built since 2007 have tire-pressure monitoring systems. The hitch is this: The system might not alert you until a tire is 25% lower than the recommended pressure. And if you wait for that, you’re wasting money, as underinflated tires reduce your gas mileage by roughly 0.2% per pound that they’re low. That might not sound like much, but try this math: If your recommended inflation pressure is 40 psi, and you’re 25% low on air, that’s a 2% hit to your gas mileage. Plus, underinflated tires wear more quickly and unevenly, reducing your tire life.

No list of gas-saving tips would be complete without the admonition to slow down. There’s no getting around the fact that lower speeds require less fuel, most because aerodynamic resistance increases with the square of speed.