As you know from my writings and sketches, I like to carry a notebook. People often ask me what types I use, or assume that I use the (increasingly fashionable) Moleskine books. I like Moleskine books (the little 3inx5in ones for example), and have used them a lot in the past, but actually I prefer the books by HandBook Journal Co., (made by Global Art Materials). The surface of the paper is more flexible, in my opinion. It has a little more tooth than standard Moleskine, which makes mark-making with pencil much surer, and it also takes wetting better,
so you can work with a little wetness as well, such as lots of ink, or watercolour (paint- or pencil-based). That allows for crisp drawings like the one on the right (click for larger view – more about these sketches here), right alongside physics research musings and computations in pen and ink line on the pages shown below on the left (those notes pertain to the paper I discussed here.)
I tend to carry one of the 8.25inx5.5in landscape ones (although I love the 5.5in square ones too). (See more chat about them here.) They allow a good amount of room to think, 
and fit a variety of drawings of various subjects. Also, if out in the world sketching people, you can hold it in portrait orientation and then use the 8.5in of the other side as a natural shield against one of your sketch subjects glancing over and seeing a representation of themselves sitting on your page.
They are harder to find than Moleskines (perhaps because the hipster set has not really discovered them yet), and so I rely on one store for my supply of them. And of course I like the solid black covers, so that means if they are out of them, I’m doomed! This happened last month and they were out of the black, not other stores had them, and I was calculating furiously and so could well run out of pages fast. I felt action had to be taken and so I reluctantly bought a green one, and got the store to order a stack of 5 of them – stockpiling is clearly the answer! Happily the batch arrived in a few days and so I was able to return the green one unused and collect my little hoard of books, pictured at the top of the post.
I’m a very happy hoarder.
-cvj
