I've been taking an online class from Cathy Johnson called "Quick Sketching in Color," and am thoroughly enjoying it. In the class, she gives instructions to make your own mini watercolor journal out of a single piece of paper.
I made mine from an 12" x 18" piece of cold press watercolor paper that I cut in half lengthwise, then folded each piece accordion-style, and glued the two pieces together to make a concertina sketchbook.
Here's a link to an Instructable on making your own concertina sketchbook.
Simplifying my kit makes it lightweight and easy to carry, and I love taking it on nature walks! I can stuff my art supplies, plus my car keys into the little bag and go on sketch-adventures.
You can learn more about Cathy's Self-directed mini-classes here:https://cathyjohnson.info/art-classes/