I wish I had an actual answer for this, but the honest truth is that nothing has been left unforgotten.
I left my wallet at home once last week and three times the week before. I've left my phone at home (or have come home without it) on an average of once a month. This weekend it was my charger at work, two weeks ago it was leaving the charger at home and needing it for work.
My keys are the closest thing I have to 'sacred', but I've left them at home when I've left with the roomies, because I can get back into the apartment and if we're leaving together or all at home, I don't always lock the door to my room.
Shoes are option, there was one memorable occasion last summer where I left for work without a bra (and that was uncomfortable).
So... shoes are pretty much it.