Look, a .223 seems great for a single overall cartridge for survival but a .308 in some circumstances might be right up there. As a survival gun I'm torn in many directons but, depending on what I think the circumstances are, if it isn't an AR (where defense would be a, if not THE, key element of my concerns) it would probably be one of these .22 Mag based guns:
Ruger All-Weather .22 Mag. bolt.
Takedown pump-action .22 Mag (in the car anyway).
Savage 24* .22 Mag/20 ga. break-action.
While a great multi-purpose-gun-in-one, with its length and weight you do NOT wanna carry this thing around (the heavy barrels should be 5-1/2" shorter).
Ruta Locura PRK .22 Mag (15 oz. folding single shot backpacking gun)
.410 is a poor survival cartridge in many respects -- they have too little energy (equal to that of a .357 Mag in general) for the size and weight.
*The Savage Combination Gun is Back
The venerable Savage Model 24 has been reincarnated as the new Savage Model 42. Long hailed as the ultimate survivalist gun on online forums, fans of the old Model 24 are going to love the new and improved Model 42.
Configured with a deadly accurate .22 LR barrel over a wickedly effective .410 bore and fitted with a durable synthetic stock, the Model 42 is rugged simplicity defined. The Model 42 is the perfect companion on long walks in the woods with your pockets loaded with virtually limitless supplies of ammo. It’s also the perfect kick-around-camp gun as plinkers can shoot to their heart’s content affordably. Being the responsible company that we are, we can’t call the Model 42 a toy, but we can say without hesitation that it’s fun as hell.