For my son's 6th birthday we had a Pirates of the Caribean party.  We were lucky that the local park had a pirate ship on their playground and decided to have it there.  I bought a bunch of black balloons with skulls on them. Then, I bought a huge parrot balloon and tied it to a tree, so it looked like it was sitting on the branches.  I found a great map table cloth and put it on the main table.  I also found gold and silver foil table cloths for the others. I put small treasure boxes (3) with gum coins and plastic jewels down the middle of the tables.  I bought a candy mold for pirate coins and made a bunch of chocolate ones and put then in clear baggies with gold ribbon tied around them. I used a treasure box that I found on sale at Target's home decor section and filled it with the bags.  I bought a pirates of the Carribean pop up play ship for $20 online and the kids loved to take turns being captain.  I also bought these great pirate canvas goody bags on ebay.  They offered free personalization so I put "pirate names" for each of the kids...you can come up with different types including left-handed pete or First-mate pete. Of course the birthday child should be Captain or Captain Jack Sparrow.  I made a great sinking ship cake. I took 2 yellow cake mixes and added bananas & candied pineapple. I made one 8" round cake and cut it in half. I used some chocolate frosting to put the 2 halves together.  You just have to play around with it with a small sharp knife to add some details.  You can pipe chocolate stripes on outside to give the look of wood.  I made a flag out of paper and toothpicks. I then put this on a sheet cake that I frosted blue.  You can make the whole thing blue or you can add a little section of island with some frosting and sugar to look like sand or colored green coconut for grass. I also made a pasta salad with tiny canned shrimp (you should be aware of any food allergies of your guests). Tropical punch and lemonade were served as drinks w/ fish umbrellas that I bought in the luau section of my party store.  I then made a treasure map and hid a treasure box made out of a cardboard box that was painted and lined with foil. I had plastic jewels candy necklaces and bubble gum coins (it was a hot day and chocolate ones sitting out will melt). I made enough clues for each child to be the leader once.  It turned out to be a wonderful party.  Having it outdoors requires you to be very creative without the use of walls for decorations.  I think balloons are one of the most important decorative tools for an outside party. "