For digital stuff it’s mostly the same idea. If it’s email (which is almost always the case), I archive and forget about it. If it’s something else, I’ll throw it in my virtual “messy drawer” which is just a folder in Google Drive.
You are getting quite a few clever ideas in this thread, but I suspect the vast majority of people out there in the real world do more or less the same as I do (of course, I’m biased).
My “philosophy” (overstatement) is that 99.99% of the time I’ll never need it. If I ever do, it might be a little painful to dig around, but that doesn’t justify having a whole system in place. I would rather keep my mess.