You've Got Mail!
Paper, envelope, crayons/markers, stamp
Teach your preschooler about how the mail system works by writing a note together. Put the note in an envelope and address it to yourself (with your child's name, of course) and affix a stamp. Then take the letter to the mail box at the post office. Your child will be thrilled to receive it a couple days later, and the two of you can talk about how it got from one place to the next.