okay here is some of the stuff i have on the boat
5 mil plastic sheet
toilet wax rings
for a larger hole i am probably screwed, but for small holes or large cracks i can take the wax and make a bead around the crack/hole and stick the sheet of plastic over it from the out side. plugs are for thru hulls, plumber putty is to help them seal. or for the shaft hole if the seal blew out.