I must say, I don't think I've ever heard of a skewer failing. I tend to take the minimalist approach, but it seems like if you're ready for that to fail, you might as well carry an extra rim as well, just in case yours cracks in half, right? And don't forget the extra brake assembly. Oh, and a set of bars in case one side snaps off.
At best, I would see the need for an extra rear skewer on bikes with more inboard mounted bearing on the rear wheel. You know, the freewheel types where the bearing re closer to the hub of the wheel. That would be a situation where I could see one coming in handy. But for most bikes, I don't forsee that being a problem.
As for a quick fix, I would check out the local hardware store. I imagine you could cobble some sort of makeshift skewer together with a bit of allthread, nuts and washers.