I have note cards taped to the door to my home so I don't forget anything important when I'm leaving the house. True thing.
Also, I have one in my archery bag for pretty much the same thing. See, there are a lot of bits and pieces of gear to put away when it's time to go home, and straight up: I like to talk and it's distracting. One day I fought some high-grade torpor and an obstacle course of TTC setbacks and got myself to the public range. (It cracks me up when I feel like I've been through this arduous set of trials to get somewhere and I realize the part that I had to play: just sitting there, being moved.) I set up my stuff only to realize: "Aw man, I left my bowstand at class." The next week, I forgot my sling. Then it was my eyepatch. When I left my limbs behind - no, seriously - I was fully shamefaced. Hence the card.
Once I got going on it, it dawned on me that I could colour-code and group the items by where they belonged in the bag, which entailed mapping out where all the pockets were, and then - I really like this bit - planning what to put in each pocket based on the order it gets taken off. Honestly, you've done things like this, right? Where you just get so involved in some ridiculously mundane project that it becomes a paragon of elegant design and gleeful geekery? Forevermore, I'll crib off my little card with deep satisfaction and a soupçon of absurd elation at its careful craftsmanship.