I have a two piece spare oar but keep it assembled when on the river and angled under the rowers seat, over the stern, so it is ready to go. I did break an oar a few years ago on the upper Sauk and just like Kyle said, I was pullin hard to set up above a chute that dropped into one of those nasty log jams. Not a big deal with two oars, but thank god my spare was ready to go and in the oar locks with only a coupla missed strokes.

King: I've floated the main Salmon in my driftboat and was required to have a spare to use the permit. Didn't need it on that trip, but you are playing Russian Roulette if you don't have one. Salmon didn't have the nasty sweepers and log jams (at least that year) that we get over here either, and it was 90 degrees instead of 40 so a swim wasn't so bad.
Driftboats aren't as forgiving as rafts, which can bounce aimlessly off the rocks and still get through, so this probably helped you as well.

I hope the beginning DB owners on this board ignore your apparent (hopefully tongue in cheek ) lack of respect for safety.