Jacob owned a long-bladed knife which he used for many of his tasks on the Island, including weaving his tapestry and filleting fish for his breakfast.

Jacob's knife as seen at Lost: The Auction.

The knife was left in the cabin after it had been abandoned. Ilana found it in the wall of the cabin pinning up a fragment of the bottom-left corner of Jacob's tapestry on which a picture of the statue of Taweret had been woven. ("The Incident, Part 1")

See also