Men: A hoodie is multipurpose. Sure, it's cozy and keeps you warm, but the hood also blocks out light if you're trying to sleep. You can keep your phone, sunglasses and passport in the pockets for quick access and it's easy to shed when you go through security.

Loafer socks are also a good bet, said Srnka. They'll save you from being barefoot in security, and come in handy if you slip your shoes off mid-flight.

Women: A pashmina is a staple, since it can double as a blanket and a way to block out light when you're trying to rest.

Fold-up flats are a game-changer. They're small, comfortable slip-on shoes that fold up in your bag. They're perfect for when you can't run through the airport in your less practical shoes.