Ninety-nine percent of the time we travel with just a carry-on. It's convenient, saves money and time on both ends of the trip (checking in and skipping baggage claim). But one of our biggest travel pet peeves is when people don't know the rules to carrying-on, namely the in-flight etiquette. So, we're breaking it down for you so you can avoid those evil glances from your fellow seatmates on your next flight.