Almost all my work originates from on site sketches. The sketches are done using grey felt pens on to synthetic paper cut into 6x9 inch sheets. Working this way allows me to capture the basic value pattern quickly and concentrate on blocking the general design. Because I'm working in grey tones, I avoid thinking too much about colour other than to make mental notes.
At no point do I use a camera. Because I spend the time to sketch and truly examine my subject matter, the value sketch not only serves as a sketch pad for resolving design issues later on but also acts as a sort of visual "short-hand", allowing me to recall more details than if I had simply taken a photograph.
I use one of those collapsable shopping bags with the cardboard sides to stow my supplies in. I just throw things in so setup and breakdown time is quick. All my gear goes in it and the bag goes with me everywhere I paint, be it outside or in a studio. Because the bag has rigid cardboard sides, it can be used as a sort of table, avoiding the need for an easel when out in the field.
When setting up my gear for a studio session, I always lay things out in the same manner.
My paper is always to my bottom left. For the final piece, I start with 140b Arches paper either on a watercolour block or wet mounted to a board or frame. I prefer Arches because it really takes a pounding and allows me to correct passages easily. My preference is hot pressed paper but I do use cold press on occasion.