Last year I typed up written instructions along with photographs of each my cats just in case something happened to us (car accident or whatever). All of my cats do not get along so I wrote a page for each cat and wrote down who they got along with and who they want to kill (i.e. my cat George wants to murder my cat Jimmy for some reason and they can never be in the same room, ever) and if they were particularily close to another cat, (my cat Tiny would be lost without my other cat Teenie) if they could somehow be adopted out together. I also included a few lines regarding the health and age of each cat and what meds if any that they are on and what food they eat. I even wrote down some of the endearing things about each cat in the hopes that it would help them if they ever needed to find new homes. For my cat Stinky, I put that her favorite thing on the planet is a little tiny stuffed bear in a ladybug suit and that she often carries it around in her mouth making a meowling sound for a few minutes each day. I figured, how could someone resist her if they knew that!
Maybe you could put something like that together. I felt so relieved after I did this because I felt like at least now, a shelter would have a good idea of who is who and what they're personalities are like and who should not be adopted out by themselves etc.. I also included the names of a few friends who happen to be partial to a few of our cats and I put their phone numbers and addresses and requested that they be contacted and given first dibs.
Of course, I hope that you and I both outlive our cats so we can rescue even more of them down the road!