I take a few road trips every year and I always use that time to flesh out ideas for writing. Most of my travel is on 4-lane highways and cruise control can handle 99% of the trip, so it's a great chance to go on auto-pilot and think.
This last weekend was no exception. I was making a presentation about Wikis to my writing group in Minnesota, and I already had that info somewhat ready to go. I maintain a wiki for my big series, and I wanted to share what I had learned about setting it up and maintaining it. I had a handout, presentation, and all that ready, so I didn't need to "practice" it as I drove. That left me free for creative thinking.
I am in between projects right now. I have ideas for 2 books, so I spent the 8 hours of drive time exploring thoughts about those projects. I dictate into a little digital recorder then transcribe when I get to where I'm going.
I now know the basic plot ideas for one book, details about the characters, their back stories, and their motivations and arcs. I tabled the other story for now and will save that for a brainstorming session with friends, coming up in October.
Not bad for a boring old road trip, right?