(Above: a monster mix and match book I made using a blank white book from barebooks.com)
One of my favorite activities to do with kids is make mix and match books. They are really simple to make and mega fun. All you really need is a couple sheets of copy paper, staples, scissors, a piece of cardstock paper for the cover, and imagination. First, fold all the papers veggie burger style and then stick the copy paper inside the folded cardstock. Next put three staples equally spaced in along the spine to hold it all together (or use another binding technique). Then cut the inside copy paper twice (one cut a third of the way from the top and the next one a third from the bottom . . . be careful not to cut all the way to the spine but it is important to be close so that it will fold easy). The rest is all about drawing. I usually do my first drawing just as I normally would, but am sure that the neck of my critter is at the first cut and that the legs or bottom starts at the bottom cut. Next I flip the head flap so that I have a creature with no head and then draw a new type of head (be sure all the lines meet up where the paper is cut). I find it easiest to do just one section at a time, so that I don't have to over worry about it all lining up.
(creature drawn on the first page of a monster mix and match)
This project is all about thinking outside the box, or playing around with the book medium (this is one of those cases where your story or pictures being in a book is paramount).
In the above mix and match I drew one of the heads so that it went on the back of the paper of another and thereby expanded to having four sections (head, neck, torso, and bottom). Playing around with mixing and matching words can be fun too. I often will use the left side to break down each creatures name, so that when you flip a flap you can go from pig to big (a pig with a bear head), or from monster to mobot (a robot with a monster head).