I don't know that I would say the conch is part of Ralph's past, as he and Piggy find it on the island, but it stands as a symbol of beauty and, more importantly, of the belief in shared authority that characterizes Ralph. The other items, a naval ship and soap, are very much a part of Ralph's past and represent order and civilization, which are at the heart of who Ralph is.
We don't learn much about Ralph's past, but the clothes he arrives at the island in become symbols of him, just as Jack's clothes do. Ralph arrives in his school sweater, pants, and a plain gray shirt, all emblems of order, rationality, and civilization. This is a contrast to Jack and the other choir boys who come stumbling out of the jungle in their long, eery black choir robes decorated with crosses and with black choir caps on their head. This associates them from the start with the deeper, darker, more irrational emotions and impulses of religion.
We also discover that Ralph's father is in the British Navy. Ralph informs the other boys that his father has told him that almost all the islands in the world are discovered and many claimed for the Queen. This, once again, identifies Ralph with Queen and country: the symbols of civilization. He is imbedded in a social order that behaves in a restrained, disciplined, and reasonable way.
In addition to soap, Ralph can also be associated with the scissors and toothbrush he longs for. He wants both so that he can cut his hair and groom himself in such a way that he remains identified with the orderly world he has left behind.