By Esther Fung

Drive a UPS truck for 23 years, and you pick up a tip or two on how to conquer heat waves.

Over his career delivering for United Parcel Service in Bakersfield, Calif., Joel Reyez has battled extreme heat more times than he can remember. He often works 10-hour shifts, frequently dipping his head into the back of the truck — which can feel like an oven in sweltering temperatures.

Like the rest of UPS's tens of thousands of drivers, he works alone, which means he's got to be attuned to any signs of overheating and pre-empt them. "We're industrial athletes," the 49-year-old Reyez says.

Battling the heat is serious business for UPS, too, which provides its drivers cooling gear, cabin fans, electrolyte drinks, water jugs and then some. It estimates it supplies more than 15 million pounds of ice to its facilities each summer to keep staff cool.

Here's how you, too, can navigate the heat like a veteran UPS driver:

Invest in high-tech wearables

UPS equips Reyez with hats, sleeves and towels made with cooling technologies developed by Mission, a brand that also supplies the fabrics to professional sports teams and athletes. But much of it can also be bought online.

Throughout the day, Reyez dips the gear into an ice chest he keeps next to the driver's seat. The water-activated technology lets the fabric stay up to 30 degrees cooler than average body temperature, Mission says. The sleeves cool him for up to two hours, Reyez says, and wrapping the towel around his neck provides a burst of extra relief.

Reyez says he is constantly urging younger drivers not to skip the wearables. Cameron Bowman, a 38-year-old driver in Waxahachie, Texas, says he opts for the cooling baseball cap and keeps an extra pair of sleeves cooled and ready for when the first pair wears off. "I change them out," he says.

Pickles are your friend

For lunch, forget the burger and fries — or anything greasy, for that matter, Reyez advises. "Would I like a big old pizza? Yes," he says. "But in the heat, that's just going to be bad for me."

Instead, his wife will make him a turkey sandwich with tomatoes, cucumber and lettuce. And she includes two pickles, which are packed with electrolytes from the sodium in the brine and traces of potassium.

"Pickles are good," Reyez says. He often rounds out lunch with fruit, and says watermelon is especially effective for hydration.

Pregame your hydration

It's not enough to drink once you're hot and thirsty. You've got to be hydrating well before that, he says.

In short, "I'm always drinking water," says Reyez, who estimates he drinks up to 20 bottles a day in hot weather. Often he's adding powder electrolytes, and he keeps Gatorade on hand in his ice chest.

To keep its workforce supplied, UPS says it has given staff more than 100,000 water jugs and installed 3,000 ice machines and 2,000 water fountains in its facilities.

Even small bursts of AC help

Every new delivery vehicle UPS purchases now includes air conditioning — a provision included in UPS's most recent contract with the International Brotherhood of Teamsters, which represents UPS drivers.

Both Reyez and Bowman, the Texas driver, got their first air-conditioned trucks this year. Before, Bowman had just two fans in his truck that blew air at "whatever temperature it is outside." Now, he says, "you have actual cold air blown on you."

Reyez also has fans set up in his truck, and UPS says the exhaust-heat shields it has added to trucks lower cabin-floor temperatures by as much as 17 degrees.

After driving so many years without AC, Reyez says he is surprised how much even a few minutes at a time keeps fatigue away.

"The AC changed the trajectory of the game," he says.

Write to Esther Fung at esther.fung@wsj.com