Since the calendar has already been mentioned, I’ll drop another of my tools.

I check my pockets every time I leave a space, and confirm I’ve got Wallet, Keys, Phone. I do this at any transition: Leaving the house, a taxi, the office, a plane.

Got kick started into the habit when I lost a big (for a kid) chunk of money. Felt so bad that I started the checks, and haven’t lost any of those three in many, many years (ง’̀-‘́)ง