The original post below is no longer valid. I have removed the “extras” only package of Cognitive Productivity with macOS from Leanpub. Rationale: Leanpub has clarified that all packages must include books. If you purchased the $5.00 “extras only” package, then you will still have access to it. But it is no longer for sale separately.
The original package of this book, which contains the book and all the extras, remains available for sale.
original content of this post
The “extras” packaged with the Leanpub edition of the Cognitive Productivity with macOS book are now for sale on Leanpub as a stand-alone package. So if you bought the book from Amazon or iBookstore, you can now avail yourself of the Extras package.
These Extras are described on the book’s Leanpub web page. I’ve also provided a bit of additional information about them in the book’s section of this website.