What's the least clumsy way to add colors to sketches you do outdoors? I'm thinking of bringing watercolor pencils and a Pentel Aqua Brush, but the thought of digging through all those pencils to get the color I want drives me up the wall.
A water brush and a little (altoids) tin or pouch with some (half) pans or dried dabs of paint from a tube seems to be working for people.
Limiting your palette down to a maximum of two colors
For some information on materials for urban sketching, you can also read The Art of Urban Sketching by Gabriel Campanario.