I'm going to bury things in sand that represent commandments to follow:

After each child digs out an object, we'll discuss what it means and how we can do that commandment. For SR, as an additional challenge, I'm going to have them try to figure out which modern day prophet talked a lot about that commandment (names in parentheses are the answers).

dime - tithing (Snow)
Sacrament cup - come unto Christ (Joseph Fielding Smith)
Heart - Love one Another (Lee)
small can of fruit - Word of Wisdom (Joseph Smith)
Missionary tag - every member a missionary (McKay)
Mini gold plates (made from felt) - read the Book of Mormon (Benson)
small shovel or spoon - service/"do it" (Kimball)
small picture of a temple - preparing to go to the temple (Hunter)
small house or picture of house - FHE (Joseph F Smith)
 

Thanks for all the help and inspiration you've shared to help me put this together!