My thoughts exactly on the thrift shops. You can also find other gear there, and even boots. While making clothing and other items will fill the time it will take energy and moisture from your system. If it really is like Tom Hanks who says there will be water or any food sources or even shade on the proposed island?
Did anyone ever see the fed ex commercial based on that movie? It was hilarious.
And ironic.

http://www.youtube.com/watch?v=COTnAYQ2nbs