It goes without saying, the French do food very well! Most villages have at least a bakery for your morning croissants, lunchtime baguette and afternoon cakes etc. Small towns will generally have a butcher, chemist and small supermarket too.
If you're going for a week or more it's worth taking a couple of hours out of your bouldering schedule and stock up at one of the big supermarkets. The biggest one, and I mean huge, is the Carrefour up near Villier-en-Biere not too far north from Bas Cuvier. Here's a link to it on Google maps. It has everything you could ever want and some! NOTE: The majority of French shops are closed on a Sunday and a lot of smaller shops in towns and villages will close at lunchtime too.
There are numerous places to eat out in mosts towns as well as various take-aways and the usual fast food outlets so you'll never go hungry.
...out of chalk?
There's an outdoor shop in Fontainebleau called S'cape that will solve all your gear needs or you can visit the new indoor wall that's opened up in Fontainebleau called Karma that also has a shop. Or if you happen to be out at the Carrefour mentioned above, there's also a Decathalon right next to it that has a small climbing section but all the essentials.
If you're needing your shoes re-soled, SOeScalade runs a resoling van at the Roche aux Sabots parking at the weekend.
...soften the landing
There are quite a few places to hire a mat in Font - www.thehouse.fr,Fontainebl'hostel and Camping Ile de Boulancourt (8€ for one day, 15€ for two days and 25€ a week) all rent pads, as does the Pizzaria in Arbonne La Forêt, randomly. The outdoor shop in apparently rents them too, S'cape, although couldn't spot it on their website.