I'm glad you reminded me of this. I used to carry a 3 foot length of 2mm cord to practice knot tying. My wife used to make fun of me tying up table legs in restaurants while waiting for dinner to arrive. I need to put that cord back in my pocket.

Also, since getting a Nook eBook reader, I now carry that around quite a bit. If I get stranded somewhere I always have a book to read. And since I don't always feel like reading, I scan in my piano music, turn it into a multi-page PDF file, and load it onto the Nook. So I can grab my MP3 player to listen to the pieces as I follow the score on my Nook. This helps greatly while memorizing pieces for performance. So I can "practice piano" while stranded away from home too (provided I also remembered to bring my MP3 player!) People with fancy eBook readers can have a reader AND music player all in one device, but I just have the Nook Simple Touch, the most basic model - book reader only.