Hey Area10.
I broke a big brand paddle during a 10 mile downwind in Hawaii a couple of weeks ago. It wasn't a fault of the paddle but of the knucklehead who sat on it while taking video/photo's of the other paddlers coming towards her.

A swell knocked me sideways from my knee's to a straddle position on the board with the paddle lying wrong way up under me. It was like slow motion as I knew it was there and the wrong way up and while in mid air my thoughts were not good. [}:)]
The paddle snapped clean in half about 2 inches above the blade join. The first question asked by the other paddlers was "have you got any duct tape?". The answer was no. We only had about 3 mile to go but had to find an alternate exit point and had to cut across wind and current for about 1.5 miles. Lucky we had a cell phone to call our driver and notify of the new pick up location. My paddling partner gave me her paddle and she paddled prone to the finish as she has good experience in that.
Anyway after wards we thought about it and thought it a good idea to carry 1 to 2 pieces of dowel and duct tape during long paddles like is. The dowel could be only 20cm long. That way if the paddle breaks you could put the dowel on the outside of paddle over the crack and then tape it on round and round with the tape. Won't be super strong to continue hard paddling but would be a good way to get you back to shore limping.
Just thought I'd share cause this experience sure did dampen a great downwind.