Toothbrush (paste optional), shampoo (doubles for soap) and a travel towel (some checkpoints had showers but no...). Learning any amount of French is good. Arm and leg warmers are lightweight insurance for cold weather.

I've always slept at checkpoints, so have had no need for a space blanket or anything else. I have always aimed at a fast first day (Carhaix for first sleep) and to cruise the rest. You get slightly in front of the main group of riders, so shorter queues, then get plenty of sleep while others are dragging themselves in.