So what is this?
My best guess is that it's part of a promotional package from the syndicate to entice other newspapers to pick up the strip. They'd get the booklet as short sampling of sampling, certainly a cover letter, and maybe a few other bits and bobs. They actually still do that today; you can see samples of all of King Features' strips here. The reason they used to send out eight (instead of five weekdays or six regular strips and a Sunday) is simply because that's how many pages they would have to print up anyway. You have to print in multiples of four, and I'm sure four strips didn't seem like quite enough.
I'd be curious to learn how many of these might have been printed up and for which strips. Did they do this for every strip in their stable, or just the ones they were trying to promote more heavily? How frequently did these get re-issued; was a new batch printed every year, every five years, just whenever they ran out..? How long was this particular practice in place? What else was included in the PR package?
See, this is why I started up this "On Strips" series of posts: to learn about all these aspects of comic strips that I've been largely ignorant of!