One item I never leave home without when travelling is a pair of ear plugs. When I’m on an airplane the ear plugs cut down on the engine noise which makes for a much more relaxing trip, they also cut down on the crying child in the row behind you (yep I’ve been that mother on a 14 hour plane trip whose baby won’t go to sleep – sorry!).
Also, when staying in hotels, you’ll often find that people walking and talking outside of your door may wake you up, unfamiliar noises that emanate from the street outside also may interfere with your sleep. A pair of ear plugs will help to eliminate these problems.
I prefer the ones with the cord, so if one falls out you can easily find it again.