Göra allt i ett med lite komponerbar DML?
INSERT INTO order_item (item_no, order_id)
SELECT
X.item_no, @order_id
FROM
(
MERGE INTO items AS tgt
USING
(SELECT TOP (@whatever) item_no
FROM items
WHERE status = 'Unused'
) AS src ON tgt.item_no = src.item_no
WHEN MATCHED
UPDATE SET status = 'Used'
OUTPUT $action as action, item_no -- $action needed for more complex stuff
) AS X
-- WHERE action = 'UPDATE' -- needed for more complex stuff