Before traveling to Williamstown I searched Chowhound for some suggestions and found very little information. Two places we ate at there were, Hops and Vines for dinner and Tunnel City Coffee for breakfast. Hops and Vines has great food but is a tad expensive. I particularly recommend having a gin martini made with Greylock Ethereal Gin. Also try the Buffalo Crisps for a unique appetizer, and finish with the strawberry rhubarb crisp.
Tunnel City Coffee is the happening place for breakfast in town. Besides quality breakfast pastries they sell pint containers with cereal or granola that are designed for adding milk. A pretty cool idea which I have never seen before.