Someone on /r/Plural asked whether they should write a manual for new headmates and this was my reply:
If you're thinking about writing down passwords, go the full mile and use a decent password manager. Bitwarden is my recommendation.
If you're bodily adult or on the cusp of adulthood, I would also keep a list of addresses you've lived at and the month + year you moved in and out, along with workplaces and the month + year you started and ended each job, if applicable. This is less for in the case of new members, and more because a lot of applications like to ask you about these things and it's tricky even for folks without dissociation/memory issues to keep track. (Keep this information in a secure location, too. Bitwarden should let you store notes in addition to passwords.) Since you mention that new headmates tend to come around during times of high stress, I'd also recommend writing down safe coping strategies, a self-care checklist, safe people to talk to, and anything else that might help you get through those times.
For the rest, it depends on whether that knowledge is something that you use in your daily life, and thus something that would actually help people feel less lost. I would start by asking newer members why they felt lost, what tasks they struggled with, and what information could have helped them out, instead of writing down things for the sake of writing them down. You want to reduce overwhelm, not add to it.
(But like, seriously! Please don't make your newbies memorize a bunch of plural community jargon and the names and roles of every one of their coworkers on their first day here! Not even singlet workplaces expect that!)
I kind of want to go back to this and expand it some into a proper essay, though we're semi-underqualified because we don't get newcomers anymore. Maybe it can be a general list of "stuff that's good to write down because your parents didn't teach you shit about how to be an adult."
(fallen london stamps by