You do not have to buy the books that "go along" with each of the downloadable books, but I decided to. They were very reasonably priced on Amazon, and just very cool books. The book recommendations are listed in the downloadable document so you can easily find what is suggested.
Here is Abigail working on her "Vermont" page of the book. She is using the correlating page in the purchased state book to answer the questions. (If you didn't have the book, you could easily find what you needed online.) Abigail was my youngest participant, but she loved working through this, and she did a great job finding the state flags, capitals, etc. in the correlating book and writing them down in her printed packet.
Here is Sidge working on Texas:
My kids absolutely loved working through these. There is coloring and writing, and each of my kids could decide how creative or detailed they wanted to be. Sometimes they really took their time and made pages look great. Sometimes they went a little faster. I was especially impressed with how well they did copying over the lakes and rivers in each of the states onto the paper. (You can see that a little bit in the outline of Texas on Sidge's paper above.)
I really suggest you check out this company on Facebook, Twitter, Pinterest, or Instagram. This is a FANTASTIC product for the price. You are getting an entire unit right at your fingertips, and if you buy the book, there is very little parental involvement at all. You can simply say "Get out your USA Activity Bundle and they are off!