Airport security line

Photo: Thinkstock

A Belt

Not only is it a pain for you to unbuckle and put it through the scanner, but it's even more annoying for everyone behind you waiting for you to take it off. Opt for pants that stay up around your waist without extra help (and we don't mean pajamas or baggy sweats).
Flip-flops

Photo: Thinkstock

Flip-Flops

Think about how many people stand in the security line at the airport. Now, think about swapping germs with all of them. "Wear socks," says O's creative director, Adam Glassman—not only will they keep your toes warm on the plane, but also they'll prevent your feet from becoming bacteria magnets as you walk through the body scanner.
Jewelry

Photo: Thinkstock

Lots of Jewelry

While a little sparkle quickly jazzes up any outfit, it isn't always the easiest thing to take off (think too-tight rings and tiny clasps). If you still want to bring jewelry to wear once you arrive at your destination, keep it in a separate bag inside your carry-on so that it's easily accessible for security. If you have particularly valuable items, request a private screening, says Glassman, to avoid becoming a target for pickpockets. And while studded pieces are certainly stylish, the TSA doesn't necessarily embrace this edgy fashion trend. Save the spikes for occasions that don't involve a metal detector.
Gladiator sandals

Photo: Thinkstock

Gladiator Sandals

This summer's especially popular gladiator sandals loaded with buckles don't make going through security easy for anyone. Boots with laces and zippers aren't much easier. Keep it simple with comfortable flats that slip on and off. And while we highly recommend looking put-together while traveling, pack—don't wear—your heels. Even if they feel and look good when you put them on, most likely they won't by the time you get through security and hobble to your gate. Plus, you never know when you'll have to run to catch a flight.
Hooded sweatshirt

Photo: Thinkstock

A Pullover Sweater or Sweatshirt

Just like a belt, you should start removing bulky layers before you get to the X-ray machine. Stick to a zip-up style sweatshirt or cardigan so that you don't have to struggle to take it off (or mess up your hair in the process). In fall and winter when you need to bring a jacket, Glassman recommends a puffy, down-filled style that folds up and doesn't wrinkle—making it easy to stuff into the plastic bins at security and fit in the overhead space on the plane.
Bra

An Underwire Bra

The wire in your lingerie can trigger sensitive airport metal detectors to go off. Opt for a bra that offers support but doesn't make you susceptible to a pat-down inspection. For a light lift, we like the metal-free Bra-llelujah All-Hosiery Comfort Bra by Spanx—it won't get you stopped at security or dig into your back and shoulders during a long flight.
Beauty Products

Big Bottles of Beauty Products

You don't necessarily wear them to the airport, but they'll definitely get you stopped. "Follow the rules," says Glassman, and lines will move quicker, and in turn, you'll be more relaxed. And skip the dingy Ziploc—Adam's favorite TSA-approved travel bag: Flight 001 Clear Zip Case ($10).