As it happens, I would classify a saw as essential. The saw on a SAK (locking prefered) or a Leatherman makes shelter building, trigger traps etc much, much easier to make. Especially if you have injuries.

Wire saws have their uses, provided you understand their limitation. i.e. You kink it, it's going to break.

Given the choice between the SAK, a wire saw or a "Rambo" knife, I'll take the SAK.