Guitar pick or pocket watch (husband).
Special coins, for example, if I get a wheat penny I’ll put in the 5th pocket until I get home.
Like the idea of putting a ring there while washing my hands (probably the entire bathroom visit). I have a number of pinky rings and they seem to want to drop into the sink when I wash my hands.
I use it most weekdays. That’s where I put my flash drive so I can bring it to and from work.
Anytime I’ve got change on me.
When I carry a watch it is a pocketwatch, and that is exactly what that pocket is designed for.
I use it infrequently for things that have been mentioned - a thumb drive, an individual key, guitar picks, sometimes coins because we have $1 and $2 coins here. I don’t carry change. So not very often, but certainly far more often than I use the back pockets. The most I ever carry in them is a few sheets of folded up printed material that I don’t feel like carrying, for instance say a form guide at the races.
I used to use it regularly to keep money for the bus separate. They needed the exact fare so knowing I had just the right combination for a couple of journeys was very useful. I have a pass now.
But I still use it every day for keeping the keyring with my work keys on it. They’re in and out of the pocket several times every day.
I have RX pills in that pocket as I type this.
Very rarely. I might stick my wedding ring in there if I’m doing a particularly dirty job, like working in the garden or mixing ground meat by hand. Or I might stick a coin in there. But mostly I don’t even remember it exists.
This. I just checked to make sure the jeans I am wearing still have one (they do). I need to try using it, but I am worried that anything in there will dig into my thigh when I sit down. I’m kind of tactilely defensive…
Another vote for key fob. As long as I have the fob in my pocket my car will unlock and start for me with no traditional key needed.
When I was young and asked what that pocket was for, I was told it was a watch pocket. Don’t know if that was true* but it’s what I was told. Later, when I affected a pocket watch, naturally, I kept it in the watch pocket. Other than that, nothing. Had to check and see if today’s pair of jeans even had one and it does but it contains nothing but lint.
*On preview, no less an authority than DrFidelius agrees.
My drugs are too big for the little pocket. 
Lately I’ve been wearing shirts with a pocket for my vape pen, though.
I used it for my lighter when I was a smoker. But I quit smoking (yay!) in January after 20 years.
As Dr Fidelius stated, (reply # 24) it is called a “watch pocket”.
Wikipedia says "A watch pocket or fob pocket is a small pocket designed to hold a pocket watch, sometimes found in men’s trousers and waistcoats and in traditional blue jeans. However, due to the decline in popularity of pocket watches, these pockets are rarely used for their original intended purpose.
I used to keep a series of small pocket watches in there. Note the plural. Very easy to forget to take them out, they go thru the wash, time for a new one.
Gave up on that and started carrying a cheap $12 Timex watch in my left pocket instead. Surprisingly, those seem to last and last and last. On the scale of 10-20 years. Very good value.
Once in a while I’ll put something small in it that would be hard to retrieve among the keys and coins.
Nothing. I don’t trust it. I would only put something in there if I desperately wanted to lose it.
I seem to recall hearing you can lick them seemingly forever with no ill effect to the watch.
I hope they aren’t suppositories.
I never use it intentionally, because I think things will fall out. I have a couple of pairs of chinos that have a similar small pocket, but it is entirely within the right pocket – kind of a small flat pocket on the inside lining of the main pocket. I like those, because then I can keep something in that pocket without it damaging my phone, which is in the main right pocket.
When I’m visiting my mother in New York, I keep the front door key there. When I’m home in Panama, my key ring has apartment and car keys and they are too big to fit. If I know I may need a specific amount of change for tolls or a tip I might put it there.
I used to do that in college, with a watch chain attached to my belt. (Ah, the affectations of undergraduates!:))
Yes, I had a chain too. Youth is wasted on the young.