In high school (And once, freshman year of college) I would routinely lock my keys in my car. Or leave the headlights on all day. Or something else silly that required either a very patient friend or my parents. Now, on instinct when I am getting out of a vehicle I grab for my keys and freak out if they aren't exactly where they should be.
I've gotten in the habit of doing the pocket pat check whenever I leave anywhere. Right front pocket for my phone, left front for my keys, back right for my wallet, back left for anything miscellaneous.
Here is something I learned from drinking: always keep your stuff in the same pockets and in the same order. In this way, you can easily check your wallet in the dark for how much money you have left, whether or not your keys are there, or if you brought a condom. Also, if you can, minimize how you do this check. Doing a self-pat can show pickpockets exactly which pocket you are most worried about and help them target you (if pickpockets are a problem where you are living).
Next Hubski meetup, if I find my wallet is missing afterward I'm gonna know where my first mistake was.