-Ralph-

Yep, as Luckypants says, take a tank bag on board with all your valuables.

Do you have a cabin? If not a couple of tips:

On the Pont Aven the reclining seats lounge is at the top of the main staircase on the top deck, next to the swimming pool (don't take swimming stuff unless you want to be the only adult in a tiny pool packed full of excited kids). Go straight up there when you board and at the back of the room is a rack containing duvet's pillows, etc, go commandeer what you want before anybody else gets there. I made myself a bed on the floor at the front of the room with one of the duvets then dumped all my towel and bike gear on top of it.

At night when sleeping I wrapped my tankbag in the towel and used it as a pillow. Nobody was getting my wallet, camera and phone without waking me up and getting a punch in the face.

There is a shower and small changing area in the toilets right next to the swimming pool for the morning.

Anything else you want to ask about the ferry or the journey, fire away.