I thought that it would be easy to make a cover for the folder and just add a couple of pockets to hold the pens etc but it turned out a little more complicated than I thought. See, if you are making a slip cover, you can't have pockets unless you have another layer of fabric to sew onto, otherwise the folder won't slip in at all.
Anyway, here it is.
It's not perfect (the back slip pocket could have been a little wider for more stability) but it does the job.Oh look, I just noticed I cut the birdie's head off -- ooops.