There are many things on Mormon’s mind. The current terrible war is very clearly one of them, as the text of the letter indicates. His son is also one, as the fact of the letter demonstrates. This verse tells us that with all of his other concerns, the records are still one of the important things on his mind. He mentions that there will be Nephites deserters because the records will have the chance to help them. Moroni is to write something that will help those people. Mormon specifically mentions that he must give over the records to Moroni. Mormon knows that he is nearing the end of his life, one way or the other, and therefore the time has come to make the formal transition of record-keeper.
Because Moroni would be the logical person to become the official record-keeper, we cannot be certain that this suggestion that Mormon has records to deliver to him indicates all of the records, or only the plates of the Book of Mormon. While eventually it was only the plates of the Book of Mormon that Moroni received, this letter comes earlier, and could have had the general intent of giving him charge over all of the records, as had the previous record-keeper to the next for generations. Similarly, we cannot know whether the command to write “a few things” refers to what we have, or the general task of the Nephite keeper of the sacred records.