I love these treasure chests which are supplied through Bookstart, which come free with children's books. My boys tend to keep their favourite artwork stored in them (although we quickly run out of room). They gave me an idea to make some smaller boxes ourselves, decorate them and use them for special 'treasures'.
We used an empty laundry detergent box, (which is conveniently shaped and opens up like a treasure chest) covered it in brown paper and drew lines to make it look like wood. Adrien decorated his with glitter, glitter and more glitter. Some coloured tissue paper rolled into balls as the 'gems', and some decorative drawings with markers.