A Pirate party is always a fun theme...The invite pictured here was purchased through Oriental Trading. It was a message in a bottle - Very Cute!
I suggest using craft paper as tablecloths...they can be used as overlays cut in large squares. Treasure maps could be drawn on each of the overlays very easily by using sharpie markers and creating dash lines to reach where the "X" marks the spot.
Furthermore, using a large treasure chest -which could likely be found at www.shingdigz.com filled with chocolate coins could be used as a "pinata". Children could be given goody bags along with a treasure map to find the treasure chest filled with chocolate coins and once they reach their destination (with adult supervision...of course) they can each fill their goody bags with the chocolate treasure.