Yes, I think a person as creative as you will want a few film holders. They arenít too costly though. Given a choice I would go for the ones with the metal dark slides if you can find them. They are a little heavier, but I have had a few plastic ones crack. Cracks and breaks arenít good at keeping things dark.
What sort of lens, mm and brand, does the kit have? At one time Peter had a bunch of barrel lenses (no shutter) from print shop equipment. He got them very cheap. Maybe he can help you expand your collection.