I always carry my jewelry with me onto planes, even the inexpensive bits, as I am attached to my accessories (in case you couldn’t tell). The rule of thumb is that you are never supposed to travel with expensive jewelry, particularly to unknown parts. And this is today, with the reasonable expectation that you are not going to get mugged on a plane. Imagine how much more fraught with peril was traveling with your gems on a coach, on lonely roads without the aid of streetlights or state troopers. This is why some ingenious jewelers crafted “coach covers”, orbs that went over your earrings or necklace to make them seem commonplace, when really they were hiding diamonds.