During the year I spent traveling in 2013 there was one item I feared losing more than my passport, more than my wallet, more than computer, more than my backpack. That item was my super-awesome earplugs.
When traveling for an extended period it's probable you'll find yourself sleeping in unfamiliar places. Sometimes these unfamiliar places bring unexpected noises, like the 5am calls to prayer in Tanzania or that time they literally completely leveled the apartment building connected to the one I was staying in in Turkey. Or maybe you'll find you need to get your sleep in while onboard a plane, train, bus or cold, cement terminal floor in Keflavik before shifting timezones.
All those situations — and many more — were made a lot easier with earplugs. I'm not a particularly heavy sleeper, normally but I was able to sleep through just about anything when I wore mine.
You can probably find the cheap, disposable kind at your local hardware store or music store, but I suggest taking a look at the Earplug Superstore. They have most kinds of ear-plugging devices you can think of — including this page dedicated specifically to earplugs for sleeping — but the ones I have and would swear by are the SilentEar brand.