You're on a six hour train from Sydney to Newcastle. You didn't bring your phone with you. The train is empty or full of people who don't speak your mother tongue. Despite your eyes screaming to be let shut, you don't want to miss your stop. That's oddly specific, but the point is: What do you think about when you're given or give yourself time just to think?
Sitting by the window, I usually look outward, wondering what life is like for either people in homes the train passes by, or animals living in the woods. Probably sounds boring to some, but for me it's akin to staring at the vast twinkling blackness of space and feeling like a blade of grass among trillions. You could also play "I spy" and try to catch people picking their noses.
I will imagine that the other people on the train are not distractions - because to be honest I could easily spend the time looking at different people and wondering who they are and what exactly in their lives has lead them to this moment (in a non creepy voyeuristic way). I think what I tend to think about (when the rare occasion arises when I am not distracted) is similar to most people - I reflect on myself. Often its easier to distract yourself than have to face yourself but I do think that when you are truly undistracted introspection becomes somewhat inevitable - at least that is what I have found.
I generally use times like that to either develop on a story idea or ponder deeper into whatever psychological or philosophical ideas I've been working on lately. That's best case scenario, if I can switch off useless mental blather mode that wants to run on autopilot most of the time. But as Moon said, if the sights are interesting I might just admire them and dream.
I'd wonder how this train is going to cross the Indian ocean, make it across Asia and Europe, through the Channel Tunnel and on to Newcastle. Also, I'd wonder why the hell I was in Australia in the first place. It's no wonder I can't understand anybody.
Probably where I am in life at that moment. I mean aside from the obvious "on a train" answer. And then I'd want to be distracted because I'm hella boring. Or I'd stare out the window the whole time like some others have said. Lots to see in this big big world.
I used to take hour-long walks in the morning for a bit of exercise and I'd work on my stories while doing so. The last time I took one of those walks I found myself mentally writing bawdy lyrics to children's songs. I may have become Homer Simpson somewhere along the way.
I'd probably be staring out the window at all the upside down Australian scenery and wondering why the train doesn't fall off into space under the influence of gravity.
When I grow up, I want to be a social infection! ETA: and I sing bawdy lyrics to childrens' songs all the time. And Christian hymns if I'm in the proper company.
No... haha. More like in the company of people who know the melody of Christian hymns and find a pornographic interpretation funny. It's a more inclusive Venn Diagram than you'd think.
If I can focus, I'll run through the next scene in the novel I'm working on or think through whatever social event or project that's coming up (such as gardening, etc.). But if I can't manage to focus, I'll probably be replaying weird scenarios in my head that will probably never happen, or ruminate over bad decisions I made or the meaning to life. I really would hope it's the former. xD
The future. Where I want to be someday and how I'm going to get there. Especially if I'm undistracted at the end of the day. Most people wish upon a star. I wish upon a sunset.
Stories. Not always what I'm currently writing, which I should try to get better at marshaling my brain into focusing on the WIPs cause when I don't I notice I don't work on 'em near as good. Sometimes the brain wanders and I go every which-a-way but when I catch myself I try to daydream out at least part of a story.