This Pirate Treasure Chest Pinata is about the best game I can think of when your party's theme is Pirates.
Just imagine how many kinds of goodies you can fill this pinata with. Get some candies covered with gold foil, of course, for this game they are called gold doubloons.
Of course, you could always make this fun party game 2 fun party games...hide the treasure chest and give each child (or make up teams) a map marked with X's and clues and let them find the chest themselves...then hang it up and let them break it open to reveal it's treasures!
When you use a pinata all you have to do is fill it with goodies and treats. Give each of the kids a little party bag to put their treasures in and you have a goodie bag they can bring home.