If you're going to buy one button up for your travels in 2018, you might want to take a hard look at Outlier's S140 Hidden Pocket Pivot. First off, the shirt is made out of 100% merino in a refined garment dyed twill. This means you have a shirt that not only looks great, but has all the essential properties of merino: breathability, thermoregulation, and it's bacteriostatic so your shirt won't stink. You've also got their game-changing pivot sleeve construction and there's also a hidden pocket where you can hide your passport and any slim item you need to stash discretely. 

$198, outlier.nyc