You could make a birthday cake in the shape of a treasure chest- Bake a cake in a loaf tin, cut the top inch or so off (Leaving it on a slight hinge) and fill the gap with chocolate coins (Pirates gold!) and then ice accordingly!
As for Princesses, cupcakes with pink sprinkles and jelly hearts go down a treat!
Savoury things.... Sandwiches held together with mini plastic swords (These can be bought at most places that sell party things), and fish shaped corn snacks (Most supermarkets) would be quite affordable and piratey!
(Can you tell I used to host kids birthday parties??! Lol!)
Bob xoxoxox