I teach a class called Post Office. I put on a “Postal Clerk jacket” and teach the kids about packages, letters, envelopes, and other highly interesting concepts. Then I have them write their own postcard, and we finish with a stamp buying roleplay. For beginners, we write the postcards together, usually to a teacher at the school or someone in the family. We had some smarty-pants kids in recently, however, and I told them to write the postcard to anyone they wanted.
Here are some my favorite responses. (Click on the picture to read it. Obviously.)