If you have an Elf On A Shelf in your classroom, a super-fun writing activity is to have your students keep a journal of the elf's daily adventures. I've included prompts for PK as well as older kiddo's. Encourage them to illustrate their page. Make the journals out of file folders and have students decorate their cover.
If you'd like to write encouraging notes once a week to your students, use the templates and have students glue an envelope inside their folder. You can also take a picture of your elf, or each student standing next to the elf and have them include that in their journal as well. I've also included a star chart students can color when they've done a nice job journaling. A set of "peppermint" days of the week cards is also included.