I've actually never been on a plane ride that takes longer than three hours. And spending three hours on a plane is a piece of cake, at least for me, I rarely travel alone and even if I do three hours is just about enough to have a drink or a cup of coffee depending if my flight is during the day or in the evening. So shorts flights are not that big of a deal for me but I have an upcoming flight from Europe to USA and that will take maybe like three times more than I ussualy travel. I can't risk getting bored on the plane and I made a small list of items I think will be useful on such flight.
Music (ipod, phone etc) - You're alone on a plane trip (at least it's very like for me to be), let's say you'll travel from Europe to North America (Canada, USA etc) that's about a 10 hour flight. You might be able to get some sleep in the air. You might not. And if you can't sleep you can always listen to music so the time will pass without you knowing. You can use or phone, or other sources like iPod for example to listen to music. Just make sure you've charged the batteries of all your devices before the flight.
Earpods - let's say you do listen music on flight. You'll need a good set of earpods. The idea is to listen to music withour hearing any other sounds around you. And you can accomplish that with a good set of earpods. And that's not all. Another reason to buy expensive ear pods is that when you listen to music the people around you won't hear you because your pods isolate the music to be just in your ear. That way you won't distract anyone else and also noone will be distracting you.
Battery bank - the flight is long, as we mantion before we're talking for like 10 hour flights. You might need and external source of some kind to power up your device. Battery banks are very usefull these days and they are cheep as well, so it's a must to have one a long flight.
Book - another good time killer is a book. It might be eBook or you might be a tradional man and you might have actual book, doesn't matter. Reading is an ejoybale activity and a perfet time stealer. When you read the time passes without you realising it. Nowadays people don't have time to read. So use your time in the best possible way and read some books while you're travelling.
Document case holder - it's always a good idea to have something like this. Your passport and/or id card and/or visa should be in one place. Look for something you like, there are a lot of choices. Me personaly, I like the leather document case holders. They look very stylish and I feel abosolute comfortable using them.
Eye mask for sleep - if you get tired from the above activities (listening to music, reading etc) you might feel the need to have some sleep. In the plane it's never dark enought and that's a problem for some people. Buy an eye mask to help you stop the light and get some rest.
Travelling can be time consuming and exhausting. Make the best of it by choosing your items to help you get trough it. Make it enjoybale and useful. Think smart!