Dewey Destin's can work well because even if there aren't dolphins out, there tend to be a lot of other birds, crabs, and such to look at. It's a counter service restaurant, place your order, find a picnic table on the dock, and they then bring your food out to you. Fish sandwich and fries runs about $8-$9. Friend baskets are a bit more, and I don't remember the kids' menu.
They can get very busy during the summer and even busier on the weekend when boaters from Crab Island come by for some food. I'd either go early, or call in a take-out order on the way there.
There's also a Crab Trap in the Boardwalk beach complex on Okaloosa Island that's okay for food but not outstanding.