All of the techniques in this book could be used with most types of surplus fabric. The most common type of material used for these types of rag rugs are T-shirts, but you could substitute bed sheets, towels or even things like shower curtains and use the same techniques.
So don’t let the materials used in each of these examples hamper your creativity! Use what you have!
I was looking forward to learning some simple rag rug techniques. The book is extremely basic. It reads more like a short blog post. There are missing instructions, for example it says “to crochet rug follow steps 1 through 4,” except there are no steps listed.