What do you think about when you're by yourself?

I think I usually daydream about certain situations or scenarios.

I create stories based on almost nothing.
I could meet someone, or only even see them, and then create a story in my mind about who they are, how we would connect, have conversations with them, and just make up endless stories from that one small encounter.

Otherwise, I usually think about my relationships, I try to make sense of the things that I think are not right in them. I also think about what I would be doing and where I would be if I wasn't in a relationship, I think about how my life would look.
Mainly, this thought continues in to me leaving it all behind and going on to travel the world. This particular thought takes up most of my "free-thought time", its what I think about most of all.