I want to start by saying I have a separate writer's workshop block, so my students can do anything writing related during Daily 5. If they're writing, I'm happy. The most popular activity is writing letters to each other. I have lots of fancy paper from the dollar store and envelopes. The rule is only 1 piece of fancy paper and envelope per day though. My students are also not allowed to give their letters to their friends during Daily 5. They put it in their mailboxes to avoid distraction. I store all my paper in this mailbox to keep it organized and easily accessible.
My students also have writing journals that they keep in their book bin if they just want to free write. I also offer many different prompts to assist them. I keep a ring of laminated picture prompts. The kids can just grab the ring and choose a picture to write about. I love reading stories that go along with the pictures. They can get so creative.
Each month I offer different writing task cards. The majority of mine came from Ms Winston's website. I print, laminate, and put them on a binder ring.
I post monthly journal prompts in clear sleeves from the Busy Teacher Cafe.
I own a long arm stapler so another popular choice is making books. My students will grab a piece of construction paper and a few sheets of white paper and I staple it into a book. My students know when it's appropriate to ask me to staple their book and when it's not (ex: when I'm working with a group or conferencing)
Lately my kids have been making joke books. They're so silly!
There are SO many different writing options in my classroom that there is something for everyone. Writing is actually a popular choice.
Around the holidays I make donated stationery available (Valentine cards, Christmas cards, etc.) This is a big hit too and the same rules apply; only 1 per day.
It's very easy to switch out my writing options each month. Last summer I printed, laminated, and prepared the options for each month. Now all I do is swap it out :)