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If you're wearing a suit, you can tuck it into the top left pocket;
If you're not wearing a suit, you can tuck it into the pocket above your shirt;
If the shirt doesn't have pockets, tuck it into the collar or in the gap between the buttons of the shirt.
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Through the gap between the buttonholes of the shirt, insert it into the shirt so that it does not fall to the ground.
It's safest to take with you or have your little friend in your care.
Poop or pee? Ditch toilet or squat toilet?
Theoretically, you could choose to wipe your phone with some wet wipes.
Make a bowel routine and take a look. There should be some indication of whether you have pathological problems.
Valuables are not allowed to be put casually, there is a train ticket, that seat is yours, and no one will grab a seat.