You have a good start on this question. The fire is most associated with Ralph since he is the one who is most concerned about keeping it burning as a way to get rescued. He is the most committed to being rescued of all the boys, so associating the naval ship with him is appropriate as well. Piggy is Ralph's right hand man, and he represents reason and maturity. If you want a symbol for Ralph's desire to be clean and civilized, it could be swimming. We see Ralph swimming in the lagoon in chapter 1, and he swims later as well. The conch is also associated with Ralph and is a symbol of order and civilization. Ralph is the one who finds the conch, and as the chief of the boys, he wields its authority. Finally, another item to associate with Ralph is the shelters. Ralph is the one who is most committed to building the shelters; he and only a few other boys put the last one up while most of the children are off playing. The shelters are also symbols of civilization and order. The primary items associated with Ralph reflect order, authority, and civilization.