For relative ez access, I'd likely go for Big Fish, Iron Hill or Harry's Seafood all by the river. In the Riverfront Market, Harry's has a stand with good fish sandwiches too. Parking is easy and free at any of those. If you need soft ice cream, get off 141 south for about a minute to Dairy Palace. Border Cafe is at the Churchman's Crossing exit for good cheap Cajun or Mexican food.
2 Jay Dr, New Castle, DE 19720
Off 495, heading South, at Phila Pike is a small, no atmosphere place called Aurea's. Right off the exit, hang a right at Darling and into the small strip mall. Prices are dirt cheap, and the food is straightforward and great. I love their Al Pastor burrito and the green sauce they have on the table is excellent.