1. Make up the rules together. You need to create a plan for regular stops on your walk to write what you notice. These could be on a count (maybe 50?) or throwing a stick and seeing where it lands, or whenever you hear a birdcall, or, or , or...
2. When you stop, look around and write the first thing that catches your eye, or ear. Or even nose. On this occasion I wrote the words down for Joe, this sped us up, got us to school on time, and allowed me to check my spelling when I got home! But it would be great to do the writing on the spot if you have time.
3. At home, copy the list and make changes if you like.
It was an intriguing exercise, encouraging him to really look and describe the world around him. It also helped motivate the walk itself. I will definitely try it again, but next time not on the way to school, so he has time to write the words down himself directly. It could be adapted to any walk; inside a supermarket, to the local shop/postbox, in the town or countryside.