Do you always carry spare undies ⌠just in case? Youâre not alone. A new survey found that nearly half of respondents carry backup underwear with them. And 70% of those who carry spare undies have had them come to the rescue. And younger generations are leading the charge, with 60% of Gen Z and 57% of Millennials keeping backup underwear just in case. The study also revealed that most people think underwear should be replaced every two years, but some hold onto theirs for much longer.