When you're away from home, even the smallest of distractions can keep you from getting to bed at your desired time. Sure, you could bring one of those sound machines on the trip, but that's just another thing to remember to pack.
White Noise Lite is a great utility app that plays relaxing sounds and can be used on your Android phone or tablet. You'll find some pretty standard sounds in the free version, like water flowing, crickets, chimes, and an oscillating fan. This app is especially useful for blocking out distracting noises at work, or when you just need a moment to relax.