Our version is simple. It's a plastic storage box. Inside I buried several little "treasures." Included are mini-popsicle sticks with our names on them, rocks, colored pasta, ribbon, and a plastic crab. I also included a couple of scoops from E's formula. (I don't throw them away.)
After they were buried, M had fun playing for quite some time.
We still need to work on the idea of not throwing sand, but this activity will be something we do often. It will be stored in our garage and taken outside when we use it.
Just a note: If you plan to make a sandbox for a little one, make sure you use play sand. It's been sanitized, unlike other sands.