Here's what I do:
I'll put something important away in a "really smart place", then a few weeks later when I need that thing, all I can remember is that it's in "a really smart place". Of course, I can never remember where the "really smart place" is. It's infuriating.
I'd like to think it's dementia, but it's been going on way too long. A more logical explanation is that there are elves living in my brain that get a kick out of making me look stupid.