I agree about the long sleeves. If I'm going hiking or fishing, I always wear an SPF-rated supplex long-sleeved shirt, even if it is blazing hot outside. Actually keeps you cooler than a cotton short-sleeve, since the sun isn't cooking your flesh. Come to think of it, a subdued, mid-weight, button-down, long-sleeve shirt with chest pockets is about the most versatile top you can have in your arsenal.

I really like the idea of wearing a photographer's vest or something like that in the summer, but I'm afraid it would attract too much attention in my usual metropolitan surroundings.