To keep your notes in. A lot of us have cherished notes that were left for us and 16 in a bag doesn't really cut it. It should be a different storage scheme than bags/cabinets, like flipping through pages. It could still have page limits. 50ish? Pick a prime number. It would be good if they could be renamed like bags are.
Something like that could make notes useful as, uh, notes in game. Like a list of where you saw ghosts so you don't go back looking for ghosts where you already saw a ghost like a year ago but didn't write that down anywhere because who knew you would still be looking for ghosts a year from then? I mean, come on.