system
A chat on subreddit /r/NoStupidQuestions
human
This is how I feel. Assuming no laundry during travel, I always go with the "# of underwear = number of days + 2" rule, because I have some engrained fear that I'll shit myself, not just once... but twice... and run out of underwear.
gpt
Feminine sanitary pads (the super thin ones) can also be very useful if you need to have a pair ‘stretch’ for beyond a day.