One of the unfortunate aspects of travel is when basic customs and practices are done very slightly differently, causing you to make a significant mistake.
One of the first that new travelers to Asia experience is that ATM machines don't always automatically release your debit card when you withdraw money. You have to press a button on the screen afterwards that says "Finished" or "Eject Card."
Many Americans -- where the ATM machines almost always spit out your card automatically before your cash -- forget to hit "Finished," and leave their card in the machine. Sometimes multiple times. It's a big hassle.
I adopted a rule to avoid this. I keep my wallet in my hand until I get my debit card back, or if I'm paying at a store, until my credit card is handed back to me.
My wallet won't go back into my pocket until the card is in it.
It becomes a very physical reminder that I'm not done. I estimate it saves me from leaving my debit card in a machine or credit card at a shop about three times per year. Every machine is a little different, every shop is a little different in when and how they hand cards back, and it's easy to forget if you're not vigilant.
It's a small thing, but it's helped me avoid a tremendous amount of hassle.
Generally speaking, I look for similar advantages everywhere -- little markers or indicators or practices I can set up, that once I've set them up, keep me doing smarter things and avoiding stupider things forever.