Audio jack for the plane
The essential one to connect the Bose headphone and to watch movies in absolute silence.
I have three of them in my bag, often I lose them, they remain connected to the seats and I make gift to the company inopportunely.
A small thing which quickly makes you pass for a flight pro to the eyes of your neighbor (generally your neighbor will have a cast lengthily on the object) interesting if you are single, the neighbor is a girl (or conversely) the flight lasts 12 hours, and that the neighbor is rather cool. (In this case you will quickly disconnect your helmet to engage the conversation) Be confident in 10 years of traveling, that happened to me only one time.