Container for sand if inside (like a cookie sheet or baking dish)
Have your child write letters in the sand.
For Kaitlyn, my 3 year old, I had her write simple letters like H, I, L, T, E, F--letters that involve only straight lines. She also does well with circles, so I had her do O and Q. She wanted to try some harder letters, and for those I held her hand and helped her make the movement.
For Brayden, my 5 year old, I had him do any letter that came to mind and also had him spell words. He can write all upper and lowercase letters on paper, so this activity in its simple fashion is too easy for him, but writing out simple words was just right. It was an activity to provide variety and texture beyond simply writing on paper all the time.
For McKenna, my 14 month old, I had her just play in the sand and perhaps gain something simply by listening in on her siblings.