For my son's birthday, in two weeks, I plan to build a wooden treasure chest to hold the goodie bags. I have the plans roughly drawn out. The box area will be 1.5' x 1'x 8". I am planning to document the build this weekend and post it to www.instructibles.com.
However, the big news I have today is that I found an authentic looking, working pad lock with a skeleton key. When I first thought of adding the lock, I figured it was going to too cost prohibitive, but with wonderful ebay, I found a few of them and they were priced reasonably.
I can't get a picture of the lock off ebay, but I will post it when it arrives in the mail. But in the mean time here is the auction listing. Ebay listing of pad lock.