Print out as many copies of the lined paper as you'd like (the first page has lines with less space in between them, the second has more space - choose whichever you prefer) and staple them together to make a diary.
Either make writing in the diary a requirement or tell students it's optional, and they can write how much/whenever they like.
Consider providing prompts - what makes you happy? What did you do this weekend? What don't you like about school? etc.
Make it homework, or do it at the end of class as a cool down.