Make a treasure chest using a shoe box
empty shoe box, paint, tin foil, tape
paint the outside of the shoe box with brown paint making wood-like patterns with thin stripes of black paint. Paint on a keyhole and some bolts to make the treasure box authentic looking.
Use tin foil to make some shiny coins and other treasures, some gold chocolate coins can also be added after the kids are finished making the treasure to give them an even bigger surprise when they manage to find the hidden treasure box later.