I think the true "survival bread" that will really last indefinitely is Hard Tack. (There is a place where they have some from Civil War times on display that is still edible.) You can check out my blog post on that if you like... (click here)
This following recipe says it will last indefinitely. I don't know, but I'm sure it would last a long time. I think it would be a good recipe to whip up if you have a little time to prepare for a potential disaster coming your way, like a hurricane, or to throw in a backpack.
Credit where credit is due, I saw this on Pinterest on this blog... (click here)