Do I have to have WiFi to read a book I have already purchased.
I have been without WiFi for 2 months camping. On my Kindle keyboard all my books are there. Is this the same on the Kindle 6?
No. Once you download your book onto the Kindle (out of the cloud) you can read it everywhere. In fact, if you put the kindle into airplane mode (no internet) the battery will last longer. Personally, I keep my Kindle in airplane mode, only allowing connections when I have purchased books or want to download books).
If you don't have internet connection at home, you can try a local library, many f them offer free internet (be careful if your purchase over the internet there as it is not secure and someone could steal your credit card info)
Also, some restaurants (notably Dennys) offers free internet though I think it's time restricted. But, if you're camping out, simply accessing their internet and downloading books already purchased should be safe enough). Personally, I keep about 100 books active on my kindle as I read different genres according to my mood.