I may also extend the idea to shelters in the city as well. The idea is to take old coloring books that still have good pages and create new ones, by taking out the good pages and stapling or putting them together with yarn, and sticking them in a large ziploc type bag with some crayons. An added idea to this is also take coloring pages from online and print them out. There are many sites online that have coloring pages that you can easily print out. I made a large coloring book for my daughter this way, which is how I got the added idea.
Some sites also have mazes, or puzzles for added fun.
Some sites print out the pictures smaller than you want. Other sites have the coloring pages but also have ads at the top of the page you don't want. For those pages just print them out and put all the smaller pages together and make smaller books. You can do an all puzzles and maze books or mix them up. Here are some coloring sites for added pages to print out.