Thanks to all who responded regarding a duck haversack.
I used the term "water resistant," in my post, which is what my Swiss wristwatch says on the back, knowling that "waterproof" is only a dream. But, as some have said, the linseed oil, etc, is good for a few raindrops before it leaks into the contents.
Have a large piece of cotton duck, and I'll make a plain haversack and see what happens, knowing it, and the contents, will get soaked in the first rainstorm. I'm thinking 200+ years ago, folks either carried stuff that didn't matter if it got wet, or put it it some pouch that kept it dry.
I've learned much and your responses have been very helpful.