[willy]

I would have the spare nut too. Not because it is likely to get damaged but because when you are doing the bob and weave trying to change it on the water things have a tendency to become buried treasure. Ask me how I know ;D
You can pick them up at most marine supply houses and definetly at a Evinrude Johnson dealer which is where I would stop. Just need your year and model.
Or you can do what I do for my motors, I right down the info plus a VIN number for it on a piece of paper and keep it in my wallet all the time. Also keep a short piece of 2x4 and a pair of needle nose pliers with the kit.