Day trips from Paris with good food options
Lyon is a little far for a day trip, unless you get a REALLY early am TGV! Closer would be the town of Chablis, with its world-class white wines, and the charming Hostellerie des Clos.
Susan Herrmann Loomis has a charming cooking school in Louviers, Normandy that is a doable day trip away, as well.
I've never been, but the NYTimes did a 36 hour feature on Nancy, in the Lorraine region east of Paris. You could easily do it in a day (only 90 minutes on the new TGV from Gare de l'Est one way). It's the birthplace of the macaroon, and Lorraine is where Mirabelle plums are from, and they're in season right now, so could be cool to check out. Lyon is also a great food destination, with more Michelin-starred chefs than you can shake a stick at. I'd recommend any of the places in Vieux Lyon (old part of town, at the bottom of Fourviere, the big hill west of the city centre) or Brasserie Georges, near Gare Perrache train station. Lots of shops in the Croix Russe (sp?) area too, although keep in mind that it is August, and many places may be closed for vacation.