Many don't realize I paint mostly in watercolor because of watercolor sketching. My primary medium was oils. On trips to Paris, and when I lived there working for Walt Disney Imagineering, I found the world of "Carnet de Voyage," sketchbook of your travels. Even before Urban Sketching became so popular, many publishers in Europe published the watercolor sketch journals of artists. There were dedicated sections in book stores for these! I even saw a great show one year at the La Poste Museum in Paris, displaying artists sketchbooks. I was bitten by the bug. I had to do this! The very first sketchbook I got was made by Savoir Faire and it has inside Indian Khadi paper. I like the rough surface and the deckled edges of the paper. These are the green and blue books shown below. Sadly, they stopped making them and I bought as many as I could find a few years ago. However, there is a nice substitute that I have had students get for my watercolor sketching workshop. Sam Flax here in Orlando carries them and the covers are brown. You could google "Khadi paper watercolor sketch book," to find other options.
Since this turned into a habit and obsession over the years, I have used a variety of books and I like all of them, Hand Book, Stillman & Birn Alpha Series, and Moleskin Watercolor Books.
This is a handmade one with a soft leather cover my husband bought for me in Rome. I love it because it's small and very light weight and fits easily in my purse. The sketch shows a view of the fortress in Salzburg, Austria from the Mirabell Gardens.