Take a picture of it before you take it off. Its pretty easy to put it on backwards...
I'll echo what No.1 said. Keep a spare in the boat. Carry the tools needed to change it.
Two weekends ago, a friend and I were several miles from his boathouse when the alarm went off. Temp was 200*. I shut it down and immediately asked, "How old is your impeller?" He came back with "i dunno." Knowing what was likely the problem we start looking through the glove box and found a spare in good shape. All we needed was tools. Had those delivered via jetski and were back riding in about an hour. The impeller saved our asses. Everyone and their dog can get their hands on a few wrenches. I would bet there is less than 10 ppl on the lake who would even know what I was talking about, much less have an extra they could loan out. Cheap insurance.