Use credit card at toll booths (peyage ?) on motorways. This is much faster than fooling around with change. Once you get into Brittany there are no toll roads.
As Pete said supermarkets are cheapest for fuel. After shop closes you can get the fuel using your credit card. Put in card and nominate how much you want and pump if dispense that amount. If the card isn't totally burned of course![]()
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