In the past I've travelled on Pride of Bilbao for three separate years on my way to southern Spain. Now I'd just as soon do the drive down through France. If, like me you like frequent cups of coffee or tea, I would tell you to take with you a low wattage kettle together with an adapter. Three pin plugs on board are continental. Also take mugs, coffee and/or tea. Restaurants on board are very good but fairly pricey.
On the return journey, it's possible to stay overnight on the dockside. Returning caravanners start rolling up by four in the afternoon for the next sailing day.