When I go off on expedition I like to take a variety of papers - several sketchpads, plus a folder of various papers, some of which are tinted, and with a variety of surfaces. Occasionally I will use a specialist pad, especially when working near home, and an excellent sketchbook that has only recently come on the market is the Derwent Panoramic book. I've started using it for certain types of subject, and it has a lovely smooth surface of 165 gsm and can be used for watercolour sketching.
This simple watercolour sketch was carried out as a demonstration on a painting course. The panoramic format is particularly useful for extended mountain ranges and coastlines when a normal sketchbook often means you need to turn over a page halfway across a sketch and add the annotation 'PTO' (please turn over), which is hardly satisfactory. With this sketchbook it really makes you think about how you are going to arrange the composition before you start.
Another great bonus is that there is not really much room for over-working those nasty foregrounds that seem to give so many of us problems. It encourages us to play down the detail. If I know there is a chance of my needing a book of this format I stick it in the rucsack. Details can be obtained from the Derwent Pencil Company.