Saskcyclist,
I agree with your approach. I figure that if I'm commuting by bike I should carry my stuff on by bike as well. When I was riding in the winter I was much more careful to wear or pack gear for most reasonable changes in weather. Yesterday when I was caught in the rain I had made a decision to skip the rain gear since I was carrying a lot of other stuff to work. Since the weather was warm that was safe and reasonable, not something I will repeat as we move into the fall. Like any outdoor activity you have to be prepared for changes.