Today I did a monochrome tree sketch in acrylic, using the 14x22" spread provided by my Stillman & Birn 11x14" Alpha sketchbook. While I feel I could have worked on this much longer, I met my goals with it and also ran out of time. Sometimes I need to remind myself that I don't have to treat a sketch as if it's a finished painting! I have so many "sketches" in my books that I later wished I'd done on canvas or a piece of paper not bound into a book.
I use the Golden Heavy Body Neutral Gray acrylics when I do these. I keep them in a plastic container that has a waterproof seal. They last for years this way. I just add more paint as I run low. Having the values premixed means I don't need a palette, and I also don't need to spend time mixing. I can just dip in and paint. The heavy bodied paints dry so fast that I can close the sketchbook pretty soon after I finish. The book is clipped to an 18x24" board, so it stays open easily. I rest the top on the window sill and the bottom on my lap as I paint. It's a very comfortable way to work if you have a really deep window ledge!
I don't do any pencil drawing when I work this way. I sketch in a few lines with light, diluted paint --- just enough to know where my basic forms will lie. Then I start blocking in the large shapes, initially working back to front, and then back and forth pushing layers and adding details as needed. I'll likely do some journaling on the left side of the page that I left blank. The S&B Alpha paper is so strong that there is no problem with painting acrylics on both sides of a page.