You're sitting in the movie theater, the previews start, and you realize the teenager in the projection booth has the audio level set somewhere between 'jackhammer' and 'jet engine.' What do you do? First, you should acknowledge that there really is a problem and you need to do something if you don't want your ears to be ringing in life after 40.
Next, you need to be armed with the fact that by taking one square of two-ply toilet paper; tearing it neatly in half; wetting each piece separately in a sink; wadding each piece removing most of the water, and then sticking them in your ears you can make a dandy temporary earplug.
You're on your own on this, of course, the right way to do it is to carry some squishy foam earplugs around. But in a pinch, when the bigger risk is your long-term hearing and you need a pair of earplugs quick, there's a functional solution as close as the nearest restroom. The problem with toilet paper or yellow foam earplugs is that they attenuate high frequencies more strongly than low frequencies. As a result, everything sounds muffled when you use them. Fortunately, Etymotic has solved this problem with their ER20 Noise Attenuating Earplugs. These reduce sound level, but do so the same amount at all frequencies, so things are much quieter, but not muffled.
Etymotic also makes musicians earplugs. These require molds made of your ear canals --- which will cost about $50-$70 --- but are available in 9dB, 15dB, and 25dB attenuation levels. We heartily recommend the 9dB level for most uses.