[System.Serializable]
public class Item : ScriptableObject
{
    public Item instance;
    public int id;
    public string name;

    public Texture icons;
    public Material material;



    public Item()
    {
        instance = this;
    }

    public void Draw(List<Item> items)
    {
        GUILayout.BeginVertical("Box", GUILayout.Width(300), GUILayout.Height(100));

        id = EditorGUILayout.IntField(id);
        name = EditorGUILayout.TextField(name);

        icons = EditorGUILayout.ObjectField(icons, typeof(Texture), false) as Texture;
        material = EditorGUILayout.ObjectField(material, typeof(Material), false) as Material;

        string delete = "Delete";
        if (GUILayout.Button(delete, GUILayout.Height(25)))
        {
            GUI.FocusControl(delete);
            items.Add(this);
        }

        GUILayout.EndVertical();

    }

}

[System.Serializable]
public class Items : ScriptableObject
{
    [SerializeField]
    public List<Item> items;
}

// Tu jak tworze te obiekty

   void OnEnable()
    {
        items = AssetDatabase.LoadAssetAtPath<Items>("Assets/Items.asset");

        Debug.Log("Items: " + items);

        if (items == null)
        {
            items = CreateInstance<Items>();
            items.items = new List<Item>();
            AssetDatabase.CreateAsset(items, PATH);
            AssetDatabase.SaveAssets();
            EditorUtility.SetDirty(items);
        }
    }

    private void AddItem()
    {
        Item item = ScriptableObject.CreateInstance<Item>();
        items.items.Add(item);

        AssetDatabase.AddObjectToAsset(item, items);
        AssetDatabase.SaveAssets();
        EditorUtility.SetDirty(items);
        EditorUtility.SetDirty(item);
        AssetDatabase.Refresh();
    }