I put junk mail in this center for students to read which is another authentic purpose. Sometimes I switch it up a little bit and attach question stems to the junk mail fliers. Students can also do sorting activities with the junk mail based on author's purpose.
I also included some books that use letter writing to tell their story. One unexpected outcome of this center is that if you include thank you cards, the students begin writing them for each other which ends up being very positive for your classroom community!