Interesting timely trivia today, September 23, 2021. In a post on a trivia, news, variety information post I received today, the featured question was: “Why is there a small pocket in your jeans and what was that used for?

I did know the use of that small pocket, for many years actually, BUT I did NOT know a further piece of Levis jeans trivia related to this pocket. The original Levis jeans only had 4 pockets on them. 2 main front pockets, the 1 small watch pocket, but only 1 right rear pocket. It wasn’t for several years, in 1901, was a second rear pocket on the left added.

It was my impression that the little pocket was for small change. ie coins and such.

Originally, it appears that that small pocket was intended for carrying one's pocket watch!
No doubt, after the years passed, the use of it for coins or small items became more popular. Now they're not even regularly added to jeans, but still, several different brands, designer or ordinary clothing companies, still keep the small pocket as a perceived feature of what jeans "should" include.