OK--some ideas. I have a 7 yo boy and he LOVES scavenger hunts. This is how we do them: Hand him a paper as to where to find the next clue (Ex. Look on the top of the big white thing that mom uses to get clothes clean--the washer-- and then put the next clue there and so on. You could have all of the paper clues be like wrapped scrolls. You could even burn the edges to make them look old & authentic. When they use the last clue to find the treasure chest (I'd probably do 10-12 clues all around the house or yard) the treasure chest can contain sacks of those gold foil wrapped coins, inflatable swords, stuffed parrots (small ones), eye patches, hook hands, etc.
Then they can use bags provided by you to make their own goody bags to take home O. each of all of that stuff.
Another game idea--Walk The Plank. Use or rig up some sort of a balance beam and do it as an elimination game.
Do the treasure chest piñata and they can add the piñata candy to their treat bags. You could make a "peg-leg" to use as the Piñara stick.
You could also do a bean bag toss game (boys love that).
Good luck and have fun at the party! The kids are going to love it!