I don't know what grade you teach, but with my 4th grade class this is the time of year that we are preparing big-time for our state's huge writing standardized test in February. I try to tie as much writing as I can into
autumn themed artsy activities, which could all be put on a BB.
I use the words "Awesome Autumn Alliteration" on a bb where kids display fall colored leaves on which they have written alliterative sentences. You could use the words "Awesome Autumn ________________ " and fill in the last word yourself.
To lighten up the writing work load, I also let the kids color a very intricately
detailed pumpkin patch picture and have a coloring contest (judged by a 3rd party). I make the kids mount their drawings on colored construction paper and I hang them up in the room. Just makes the room look more festive, but not "Halloween-y"!
You could also do a pumpkin glyph (use the ellison cutter to make pumpkins) and display the results with the words "Our Perfect Pumpkin Patch."