I spent some time in New York yesterday walking around with my girl. While the goal was to see one of the fabulous camera stores in NYC, I also wanted to spend time just walking around the city.
I ran across several interesting scenes that would have been great shots, a sad looking man selling comedy tickets, a photographer photographing a couple of models (male and female in business attier), but I didn't bring my big camera with me, as I didn't want to have it's weight on me while I walked around. But, fortunately I had my iPhone with me. It has a pretty good built in camera, not the same as my 5D, but it will do well in a pinch.
As I wasn't making a photo walk, I was just walking around in the city, I found this to be a great option. Use what the camera you have with you and don't complain about having the wrong camera. Just use your eye to take the right picture with what you have, not what you wish you had.