We have had good luck at Swan River Seafood Restaurant in Dennisport. There are better places for seafood, but we have taken my daughter there multiple times.
Sundae School in Harwichport has a treenut allergy safe area - separate ice cream, scoopers, etc. Definitely a highlight since their ice cream is outstanding.
Welcome to Holliston. Stone's in Ashland has excellent pub food , craft beers, etc. Similar to Matt Murphy's in Brookline.
You can do well if you cook. Holliston Superette has great meats, Boar's Head deli, and fish from Captain Marden's. You can order specialty cuts as well - I ordered a whole pig for a pig roast one time. Wine Shop for cheeses. Whole Foods and BJs are nearby, though I have done quite well at the Ashland Market Basket for produce and meat. Also we have several decent farm stands in town and a local beekeeper.