Found this thing in my filing cabinet, this is a DIY 35 Film Organizer, just using a hot glue gun to glue 3 empty film containers together, and label it with a bold marker pen, won't take you more than 15mins to do it. But this small little thing can save you a lot of troubles during assignment.
I use this to organizer my films stock during shooting weddings, so I know how many rolls of film I bring for a wedding. Of course, usually I bring 18 rolls of film for a wedding, even tho I not always shoot more than 12 rolls.
All I need to do this load the film into my camera according to the number on the film organizer, and store the exposed film back to the organizer, so I know how many rolls I shot, how many unexposed rolls balance, no more worry about losing count of how many rolls shot and how many rolls of film balance, or worst, exposed film get lost.