I chanced upon this book at a Waterstones shop a few months ago called Zen Origami, written by the well-known origami creator Maria Sinayskaya. It is a really nice book containing designs and instructions for 20 different modular origami projects, as well as 400 pieces of folding paper in 10 different patterns. A perfect size for taking with you on a journey!
The first project I have done (over the course of moving house and getting settled into my new job!) is the Isolde Sonobe. Many Sonobe units can be interlocked together to form larger modular objects, and the units themselves can be varied for different designs.
I folded the pieces using purple-patterned paper and attached to it some twine, beads, and Yoshizawa butterflies.