Back when I was young, which sometimes seems an eternity ago, someone taught me the "before closing the front door catechism." It consisted of saying, "testicles, spectacles, wallet and keys..." while physically touching the places they were located on my body. It works. After more than 60 years on earth I've never locked myself out of my domicile. But in recent years I've made a couple of changes in the routine. Now I include "iPod and earplugs" at the end of the list.
Why earplugs? Because I still can hear 12 kHz test tones (most recent test a month ago), and I'd like to keep it that way. It's amazing how many situations I encounter out in the world that call for sound level attenuation. And if you don't have earplugs readily available, your hearing suffers. I can't tell you how many times I've resorted to earplugs in movies, and once I get on an airplane the earplugs or sound-isolating in-ears go on and don't come off till I reach my destination.
Which earplugs do I favor? Over the years I've tried almost every type and I usually gravitate toward the passive noise-blocking soft triple-flange variety available from companies like Etymotic and Hear Now. Etymotic also has some "active" earplugs that employ noise cancelling, but I've never tried those. For my needs the passive varieties have always worked quite well. As with in-ear monitors, the most important thing is a comfortable but completely sealed fit for maximum effectiveness.
The reason I include an iPod in my list of "must haves" is less for its ability to play music than the apps inside. For me, the must-have app is an SPL meter. The question, "Exactly how loud IS that?" is one that I have constantly rattling around in my brain. I keep three apps on my iPod Touch to keep me informed - Decibel, Decibel Ultra, and Audio Tools. There are probably others, given the way apps tend to proliferate, but these three give me more than enough choices. Etymotic also has a new app called, "Awareness" that features "programmable noise isolation" when listening to music via Etymotic noise isolating phones. While it doesn't offer more isolation, it does allow you to blend in outside noise to reduce the isolation so you can hear outside noise, which would be handy if you need to hear when your plane is landing...
So, the next time you leave home, think about adding earplugs and an iPod with and SPL meter app. Your ears will thank you for it.