One very unique thing, and a disappearing tradition, are the 'Routiers': fixed-price, fixed-menu lunch roadside family-run restaurants/bars. Great value!! They typically include an appetizer (soup or salad), bread, a main course, dessert, cheese, coffee and wine.
There are no menu choices whatsoever... a lunch "surprise" par excellence!! For one memorable meal, we had a lump of the most dog-food looking, yet the most delicious, homemade pâté de foie served on a plate to share between the 4 of us, as an appetizer. The main was a 'rosbif' (beef roast, not a Brit), with potatoes. We shared a big carafe of a not-bad-at-all red wine. The meal ended with 3 different local cheeses on the massive cheese board, a piece of homemade cherry pie, and a coffee. We barely rolled ourselves back to the car that time. We've had as good, and not quite-as-generous other times. But each 'Routiers' we tried was its own foodie adventure!
The more traditional 'Routiers' experience has the soup placed in a tureen for the table, platters for the main course, and a cheese board that moves from table to table. Condiments, like pickles, are also passed from table to table. Wine and water carafes are simply placed for the table to share. You get up to fetch if you're missing something. Lunch is served at a very specific time and when the seats are all filled and the food gone, that's it. The 'cuisine traditionelle' meals usually cost 12-15 euros per person.
You do have to wander off the beaten path a bit, to stumble onto a genuine 'Resto Routiers'. They exist for truck drivers ["routiers"] and other workers who are on the road. Not all 'Routiers' restaurants are created equal, they do vary a bit we've found, with a few having little character.
These restaurants are identified by the "Les Routiers" symbol:
http://www.relais-routiers.com
During a five-week road trip, it became a badge of honour for us to find these 'Restos Routiers'. If you're doing any driving, try to find one.