I actually made these Chocolate Coin Cookies for Hanukkah but you could easily use them for gold coins in a treasure chest.
http://www.familycorner.com/family/k..._cookies.shtml
Maybe buried treasure spaghetti (and meatballs as the treasure). Breadsticks can be swords.
Mac n Cheese is "gold" colored if you make it with yellow cheeses. Serve in a treasure chest.
Blue Jello for water and add gummi sharks to it!
I hope that others can share more ideas.