public Sprite sprite;

public Item(Sprite sprite)
{
    this.sprite = sprite;
}

public Sprite spriteWood;
public Sprite spriteEmpty;

public Item empty;
public Item wood;

void Start()
{
    empty = new Item(spriteEmpty);
    wood = new Item(spriteWood);

    Debug.Log(empty.ToString());
    Debug.Log(empty.sprite.ToString());
}