I have traveled to hunt some, here and there. Often do have "backup" irons on my rifles, just in case, and in fact have deliberately made several hunts using only iron sights, from northern Canada to southern Africa.
But one thing I have observed among the many other hunters encountered during those trips is that those who insist on backup irons often don't shoot with iron sights very much, usually because they've been hunting with scopes for decades--as have most hunters these days. Which makes the value of the backup irons debatable.
If I'm going to take just one scoped rifle on a travel hunt, then I always have another scope along. Used to just take the scope and the proper tools to change it into the "primary" scope's rings--and had to do that a few times, including on my very first trip to Africa, when a new, expensive 3-9x European variable went crazy. Finished up (including taking my first kudu) with the well-used 4x brought along as backup.
For quite a while now, however, I have done what GF1 described for his recent caribou hunt--take along a smaller, second scope in the same detachable mounts as the primary scope, and already sighted-in. Even one of the 4x scopes that so many modern hunters have no use for is far more effective than irons for a hunter who doesn't use irons much. And the detachable mounts don't have to be expensive, either. The "Old Ugly" Weaver rings work very well. A small backup scope doesn't take up much room or weigh much, so can easily be carried in the hunter's pack, even a small daypack.
