When working with clients, I wear a polo with my logo on it, khakis, VFFs, and, if it's cooler, a polar fleece jacket in a coordinating color. My treatbag is ever present on my hip, as is my clicker.
If you see me when I train *my* dogs in public/classes, it's either the above uniform, or nice jeans, a plain tshirt (with or without a long sleeve shirt underneath), and clicker. Hoodie if it's cold, sometimes a training vest.