When packing for a flightmost travelers think of essentials like passports, chargers and headphones. but travel experts say there’s one small item that can make or break your travel day. It’s light, inexpensive and fits easily into your carry-on, yet few people remember to bring it until it’s too late.

From breezing through paperwork to avoiding unnecessary airport delays, this tiny travel hero proves that sometimes the simplest tools are the most important.

That often overlooked item? A pen.

While speaking to Travel + Leisuretravel adviser for tour operator Travel HeightGeorgia Fowkes, said a pen can be especially crucial on international flights. She shared that she once found herself in a bind while traveling to Tanzania.

“I landed in Dar es Salaam after a red-eye — immigration hall packed and buzzing — all of us funneling off the plane, and by the time I reached the counter every pen was gone. Dry, vanished, even the chained-up one,” she recalled.

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“There I was, holding up the line, with the rest of the no-pen folks, waiting for my turn to borrow one. Not my finest travel moment,” Fowkes added.

She continued, “People assume there will be pens waiting at immigration. Maybe, but with a few hundred passengers hitting the counter at once, those pens disappear fast. Sometimes I land at odd hours, like 2 a.m. or 3 a.m., when even asking to borrow one isn’t really an option.”

A pen can also be a life safer should your phone die, according to travel writer Roberta Bernstein in a piece for Reader’s Digest. It allows you to jot down addresses, directions or notes when you land. It will also help you entertain yourself with things like journaling and crossword puzzles should there be any issues with the in-flight entertainment system.

As to what kind of pen to bring?

It’s always best to go with a basic black or blue, as most official customs form don’t accept any other colors. Ballpoint pens and gel pens are also your best bet, as pens with waterier ink can bleed more and are more likely to cause mid-air mishaps, per Bernstein.