My oldest wore a pirate costume for the majority of the week. We had picked it up on sale last year after Halloween for next to nothing.
My mom created this huge pirate ship out of cardboard boxes. This DIY pirate ship had a simple design with some port holes and a skull and bones flag. She used a plastic paper plate holder as the steering wheel. Note the anchor below drawn on the side of the ship. The ship was a huge success. We had to tell them it floated away on an adventure because they were so upset to see it gone at the end of the week.
My youngest was involved in the fun as well. An old box was transformed into a treasure chest with a little help from some gold paint and black electrical tape. My mom found this website to be the most useful for activities and crafts: http://makinglearningfun.com/themepages/PiratePrintabels.htm They have exceptional printables, math games, reading activities, and crafts for all ages of children to enjoy.
Here he is mopping the deck with his parrot. This great craft can be found at http://familyfun.go.com/how-to-videos/familyfun-parrot-for-pirate-762365-v.
A crumbled up piece of brown paper with paths and markings inside and outside the house served as a treasure map. He completed about three treasure hunts throughout the week and found some pirate gold and golden necklaces. He was very excited about his pirate "booty" and giggled at the double meaning of the word. Aarrgh!
Parties I linked to: