Some of the bigger supermarkets like E. Leclerc and Carrefour if you find a decent size one are pretty good for cheese, booze and of course bread. Thats all you need in France.
Most tiny villages will have a bakers and a few other little shops and oddly always a hairdressers. Im sure Ive even been to villages with virtually no houses that still had a hairdressers and a bakery. In fact if your looking for somewhere for the night these remote quiet little villages quite often have a little Aire. That time of year you may well get it to yourself. Sometimes a better option than staying in the Aire in a "hot spot" town or beach resort.
If you go for a drink, pick a local cafe or bar that the locals drink in and not one in a tourist hot spot and go in and drink at the bar, its cheaper. Wine is (or was the last time I was there) about half the price it is in a bar here but beer can be pricey. Dont drink coffee so no idea on that one.