This is a rural area so opening hours are not the same as in town. Quite a number of cafes and small restaurants serve lunch but not dinner. Even if they open at lunchtime and evening they will usually be closed in the afternoon, so don't expect to be able to pick up a pizza at 5pm! Some are seasonal and others open all year round but only certain days, so it is always best to phone for a reservation. (I can do that for you if your French is rusty)
At great personal sacrifice I have tried out some of the local restaurants and have written my comments!!! Bear in mind that I may only have been there once and that my experience may not be typical.
Obviously if you decide to visit any of the big towns (Niort, Parthenay, Bressuire, Fontenay-le- Compte, Chantonnay) then you have plenty of restaurants to choose from, though some of these are also seasonal.
Coastal resorts (La Rochelle, Rochefort, La Tranche, etc) are choc-a-bloc with eating choices in summer, less so in winter.
If you visit Puy du Fou or Futuroscope both have restaurants and snack bars on site.
The French like to picnic and so there are 'aires' scattered around and at most tourist sites you will find picnic benches and sometimes a BBQ pit.