This was an activity we did last year at Cole's birthday party. We had a Carnival Party and I used our sandbox as treasure hunt site.
Treasure Hunt Supply List: toilet paper rolls, pipe cleaners, wrapping paper, small prizes
Begin by stuffing your prizes into our toilet paper rolls. I used small bags of Legos since those are always a hit.
Make sure you have enough for all your party guests.
Wrap up your toilet paper rolls and secure the ends with pipe cleaners.
Bury your prizes just under the surface of the sand and start digging! You might want to be sure to count how many prizes you've actually buried so that you know when everything has been found.