If you are looking for a bargain (furniture, briac à brac, cloths, games, books, etc), apart from Vide greniers (car boot sales) in France, you can visit Emmaüs, a French charity shop.
Emmaüs is a homeless charity founded in 1949 in France by the Priest Abbé. It provides homeless people with a home and work, usually collecting, sorting and reselling donated furniture and household goods.
To find the nearer Emmaüs in your area, look in the yellow pages and search for “Emmaus”.
Emmaus in Rennes is 49, rue des Ormeaux. It is open Wednesday and Saturday from 9 to 12 and 2 to 6pm. Thursdays from 2 to 6pm.
Emmaüs will be happy to receive any items you don’t want anymore.
You will definitely find a bargain there!