I fly somewhere between 340-400K KMS each year, and that (obviously) implies spending hours on planes.
Although I tend to work one way, often catching up on the deluge of eMails that piles up in my inbox, I try to take some time and recharge on the way back.
In my case, this involves writing music. For me, it's not only a great way to stimulate a completely different part of my brain, there is something about the process of creation that is all consuming and makes time pass very quickly.
I carry a very smart little keyboard from CME called the xKEY. It is low profile, fits in any knapsack or shoulder bag alongside a laptop, and yet is velocity sensitive, complete with after touch. In fact, all you need is an xKey, a Laptop, and your favourite DAW, and you have a fully functional recording studio at 40,000 feet.
On the flight back from London yesterday, I spent some time on a new piece of music, enjoying and leveraging some fantastic instruments from Edwardo Tarilonte in addition to a new vocal instrument from Output, called Exhale. I would recommend you checking both of them out. I have barely scratched the surface of these libraries, and they are unreal.
So for what it's worth, here is the track that kept me occupied on the 7.5 hour flight across the atlantic yesterday, as did the unbelievable "alien" clouds (as you can see in the picture below). Caveat: the piece is still very much a work in progress.