Stick to a routine
Panic sets in when you momentarily can't find your passport while traveling abroad.
Advice: Take the extra second to put it in the same place in your wallet no matter how rushed you might be in the situation.
There was a lovely gray-haired woman in her sixties who held up the tour bus for fifteen minutes while she frantically went through her main luggage stored underneath. That is after she had searched her purse and carry-on multiple times and checked in the restroom of the restaurant. Finally, she discovered that she had put in the pocket of her pants earlier in the day after pulling it out of the hotel safe. You could see the relief on her face, and her shoulders dropped considerably.
It happens to the best of us at one time or other. That's all we could tell our travel friend as she embarrassingly went to her seat questioning if she should be traveling anymore.