This notebook uses Rite in the Rain's specially treated, fully recyclable paper with their "universal" pattern, which is a wonderful combination of lined and gridded, making sketches and writing equally easy and readable.
The Seattle on-site architect's dream notebook.
This notebook splits the difference between the huge and the small. It's big enough for useful sketches, but small enough to fit in a small bag.
Because it's their all-weather paper, you won't have to worry about sweat or rain being any trouble.