India, May 8 -- I'm lucky enough to take a European trip at least once a year, and after years of traveling carry-on only, I've become the friend everyone texts before their overseas getaway. Whether it's showing up in brand-new shoes that need breaking in, stuffing your suitcase with clothes that don't mix and match, or traveling with a bag that screams "pick me" to every pickpocket in Europe, most carry-on mistakes are easily avoidable. And honestly, I've made most of these mistakes myself, which is exactly why I'm so passionate about helping my friends avoid them.

Here's what I've learned: smart carry-on packing comes down to investing in a few key items, like quality toiletry bags, secure anti-theft crossbodies, and a reliable hardsh...