Kikkerland 3-Way Headphone Splitter
Because my wife runs a dance school that competes across the country, there are lots of times we have to make road trips with a few kids in the back seat. Sometimes one of them will have an iPhone or tablet, and they’ll all want to watch a movie on it or listen to terrible music or whatever.
It’s just a little plastic doodad that hooks into a typical 3.5mm stereo-mini jack and splits the audio between three sets of headphones. Doesn’t cost much, works well enough for us. It’s also got a little chain attached to the cap so you can keep it on your keychain or a backpack zipper.
Get it for $12 on Amazon.