This 4th of July means “road trip” for millions of us: AAA estimates that 42.3 million Americans will travel 50 or more miles from home this holiday week (most of them by car), up nearly 5% from last year.  But with gas prices hovering at around $3.40 a gallon (lower than last year, sure, but still not that cheap!), that road trip could get pretty pricey — unless you know the best ways to save.

So, while we all probably know the basics about how to save money on gas — don’t crank the AC (as if that’s an option this summer!), don’t tool around town aimlessly (duh!) — here are some lesser known ways to cut the cost of gas this summer:

1. Buy discounted gas gift cards
Sites like PlasticJungle.com and GiftCardGranny.com sometimes sell discounted gas gift cards for gas stations like Shell, Gulf and Mobil.  This means you could get a gas card worth, say, $100 but only pay about $95 for it. That’s $5 in free gas!

2. Drive like a sane person
Sure, traffic jams, slow drivers in the left lane and rubberneckers may make you crazy.  But “angry driving” — like rapidly accelerating — can cost you big, says Kelli Grant, the senior consumer reporter for SmartMoney.com. “If you peel away from a traffic light like you’re in the Indy 500, you’re going to pay for that,” she says.  In fact, in a test by Edmunds.com, accelerating slowly from a green light and stopping gradually for a red light cut fuel consumption for someone driving a Land Rover by more than 35% and for a Mustang more than 27%.  Furthermore, the study found that cruise control is the way to go on the highway: A Land Rover got roughly 14% better mileage using cruise control set at 70 mph compared to a driver cruising between speeds of 65 and 75 mph; for the Mustang, it was 4.5% better mileage.

3. Strategically time your trips to the pump
During a regular week, you want to fill up your tank on Wednesday or Thursday before 10 a.m., says Chris Faulkner, president and CEO of Breitling Oil and Gas, a Dallas-based independent oil and gas exploration and production company.  The reason: “Gas prices rise on Thursdays in anticipation of weekend travel” and “10 a.m. is when most station owners make their price change for the day,” he writes.  “Unless it is an emergency, do not buy gas Friday, Saturday or Sunday.”  During the holidays, some experts say that prices could rise in anticipation of more drivers on the road. So, see tip #4 below for finding the best prices before you fill up this 4th of July.

4. Use your smartphone
Use the AAA Triptik or GasBuddy apps to find the cheapest gas in your area, says Grant.  You can also use your smartphone (the Maps app on the iPhone, for example, shows you traffic) to check the traffic before you leave the house so you can avoid gas-wasting backtracking and idling.

5. Consider a gas rewards card (your grocery store might even offer one)
If you drive a lot, it may make sense for you to get a credit card that rewards you for buying gas. To see if one makes sense for you, check out NerdWallet.com, where you’ll enter in your spending, and it will recommend good credit cards for you.  (NerdWallet.com also just launched a site to help you find cheap gas in the area.) However, it’s important to note that most rewards cards carry high interest rates, so unless you pay off your balance in full each month, these cards probably aren’t right for you (instead, look for a low-interest card).  Furthermore, “grocery chains like Safeway, Kroger and Winn-Dixie offer gasoline rewards programs,” says Jim Toedtman, editor of AARP Bulletin, which publishes a list of gas saving tips. “Get friends and family to share the card so points pile up faster,“ he adds.  However, it’s important to remember that the price at that gas station might not be the best price out there, so even with the savings it might not be the best deal, says Grant.

If you're savvy about where and how you fill up your car's gas tank this summer, you can save big. (Image credit: AFP/Getty Images via @daylife)

6. Don’t let the engine idle too long
“Don’t let your car idle, either when you warm it up or when you are at a standstill,” Faulkner writes. “If you’re going to be standing for more than a minute, running your engine wastes more gas than restarting the engine.”

7. Pay the right way
Some gas stations charge a premium to pay with credit cards to offset the processing fees that the credit card companies charge them. So, if you want to pay with a credit or debit card, “look for gas stations where paying cash costs the same as using a credit or debit card,” says Faulkner.  If you’re having an attendant fill up your car, double check with him to ensure that “if you are paying by cash, that ‘cash’ is noted on the pump, he adds. “You could lose $.05 a gallon if he mistakenly presses ‘credit.’”

8. Do the proper maintenance
Keeping your tires filled with air and your air filter clean can help you save big. “Under-inflated tires can lower gas mileage and affect the handling, braking and tread life,” says Robert Campbell, senior VP of operations at Express Oil Change & Service Center. The reason: “When your tires don’t have enough air in them, their rolling resistance is dramatically increased and it simply takes more gas to get anywhere,” says Faulkner. In fact, you could improve your gas mileage by up to 3.3% by keeping your tires inflated to the proper pressure, according to the Department of Energy.  Furthermore, “cleaning air filters in your car can improve your gas mileage up to 7%, which can equate to a savings of about $72 for every 10,000 miles,” says Xavier Epps, the founder and financial adviser at XNE Financial Advising, LLC.

9. Be picky about where — and how — you fill up
“Avoid the convenient gas station on the side of the highway as you drive home from work, which can be up to $.15 more per gallon,” says Faulkner.  And even though warehouse clubs like Costco often have low prices on gas, they don’t always — so check that gas app (see tip #4) before you just automatically fill up there, says Grant. Furthermore, don’t just automatically go with the premium gas. “Confirm with your mechanic what octane gasoline your car’s engine really needs,” says Faulkner. “Most car engines do not require high octane though the manual will say it’s ‘recommended.’”

10. Don’t tote around your entire apartment
OK, this sounds totally obvious, but people often don’t think about what’s in their car.  Bottom line: Don’t lug around a bunch of crap in your car, as “every 250 extra pounds eats up an extra mile per gallon of gas,” says Faulkner.

For more tips on how to save money on gas, check out this piece from moneycrashers.com.