Squiggles are a great way to get your "I don't know what to write about" students writing!
Have the students create a picture based on the shape they see on the paper. They can create anything they want! When they've finished drawing they then have to write a story to go along with their picture.
For my students, the rule is draw with a pencil, write a well-thought story, and then color. They LOVE this activity!