I often work in a watercolor sketchbook when traveling. I've tried different watercolor sketchbooks over the years and couldn't find one with decent paper so I resorted to making my own. I've learned there are some major advantages to this - mainly that if I wait until I get back from my trip before having the paper bound into a book, I can leave out the paintings I didn't finish or I didn't like! I can also arrange the pages in the order I like.
I'm teaching a workshop in New Zealand next February. I've posted instructions for my students on how to make a watercolor sketchbook on my workshop blog. If you're interested, check out "Making a Watercolor Journal" post at http://paintnewzealand.blogspot.com/