From St-Malo down to the Pyrenees sounds great ,vistit Bordeaux + wine sites , lots of beaches and lakes further down , Arcachon , Dunes des Pyla is a must see!
More inland the Dordogne region is nice ( as most off France )
But busy in the summer-school vacation!
On what to take it's better to read some existing posts and extract things that come handy for you.
Things i take may not work for you at all....much personal wants and needs.
Things like obligated fluo-vest etc...you can find online.
For RHD the toll-tag comes handy on the autoroutes -peage