It's quite true that one of the great boons to hiking long distances is the time to think freely and openly- but when you're not used to doing this it is quite a change.
As an avid reader I had a distaste for Audiobooks, and still do to an extent, but it can be a nice way to get in a book. My current style usually precludes carrying a book, which I used to do all the time. There used to be a "book library" on the AT, hikers would leave finished books and take new books at the shelters, but e-books on devices have largely eliminated this.
Music is a big part of my life, and this is no different on a hike. At home I often listen to music in the background, but while hiking I have the time to listen more fully and completely. The peace of hiking compliments the music and both are undertaken more completely as a result in my opinion.
Scott Jurek cites a study in his book that shows that a half hour of music has the same effect on the body as taking two aspirin. I think Malto and many others would agree that music can be an essential part of a hike if you allow it. Someplace on here we have also discussed our various "hour of power" or "long songs" playlists that a few of us have for those times you need to break out of mental rut or cover a few more miles towards the end of the day.
I also agree with others- during dawn/dusk it's best to leave the music off. I'd be a liar if I said I didn't occasionally have some days where music played all day, but I also have occasional blocks or even trips with no music. You'll find your own balance.
Reading the trail journals is always a nice bonus to hiking the AT, keeping your own, or notes on a smartphone can be good too.
I may even know a person who wrote a book while walking around.
Most will want to stop here, as this is where we board the crazy train:
As DW mentions-meditation and spirituality are excellent things to focus on in regards to filling your time. It doesn't have to be religious by any means, but hiking is a good time to debate with yourself such questions if you care to. Regardless of if there is a fella that owns the place or not, nearly any mindful practice, physical, spiritual or religious, involves some meditation.
At night, before going to bed, is an excellent time to practice meditation. It can take some time and effort to do. Generally it is active: mindfully keeping your effort focused on a something, even as simple as reviewing your day. Or passive: seeking stillness- allowing your mind to quiet and have no thoughts. Each effort increases awareness of yourself in some way.
At some point you will be able to extend this practice to walking;
You may use the motion to actively and deeply explore thoughts, emotions, or questions.
Or you may use the motion and rhythm to increase stillness and extend awareness, first of yourself, and eventually to your surroundings.
When folks talk about "healing" often it is simply actively allowing yourself to relive, feel, confront and let go past pain. In various meditation practices you may be taught to ground these issues and let them go. A hiker does something similar as they take each step. The long green tunnel in particular practically forces you into this path, failure to walk it forces many off the trail.
Whither they talk about it, know they do it, formally try, or care to define it- I know most long distance hikers practice some form of meditation. It is inevitable when confronted with yourself and nature for hour after hour, day after day. Especially as skill and experience increase and require less of your time and direct attention. It can be a powerful tool for pain management and other difficulties encountered. There are always challenging portions of any hike, being able to overcome internal and external forces that can end a hike is a hallmark of any successful long distance hiker. So much so that I don't consider it my opinion, I consider it a fact- just one that is not talked about as often as it could be.
People do get hurt, run out of money, or have external issues that delay or end a hike.
The vast majority of hikes end though for internal reasons, no hiker lasts long without facing this issue- however they do it.
You may even occasionally be so lucky as to enter your surroundings so completely as to flow with them, through them, in them, with them-become a part of them. Move with so little trouble that your hike is effortless. Crazy or not- this is the reason I hike.