1. Noise Cancelling headphones (or earplugs)
Airplanes are loud. Good noise cancelling headphones can cut the engine noise down significantly, making the whole flight a lot more relaxing. They won’t help with the crying baby, or talkative neighbors, nor are all noise cancelling headphones the same. Check out Why Headphone Specs are Worthless and Noise Cancelling vs Noise Isolating Headphones.
My pick is the Bose QuietComfort 20 (though the over-ear 25s are also good). Best noise cancelling available right now, plus they’re tiny.
If you don’t want to invest in some NC headphones (the cheap ones are rarely worth it), some ear plugs are certainly a cheap alternative. Not quite as good, and not nearly as comfortable as the QC20s, they’ll at least dim the din.
2. USB cable
Many new planes have USB plugs at every seat. They won’t recharge your phone/tablet very quickly, but they should keep it from running low. A cable long enough for you to still use your phone comfortably, or store the phone in the seat pocket, is ideal.
Not all USB cables are the same, however. Some don’t let your phone charge at it’s maximum. Check out Wirecutter’s pick for some cheap cables that do.
If you’re an Apple user, this counts for Lightning cables too (as they’re basically just USB with an expensive connector).