I can’t remember the last time I got a foreign or old coin in my change, but it must happen to people, because I often find them on the shelf at the coinstar machine - people tend to leave the rejects on the shelf - and I pick them up - I have an old sweet tin with a collection of a couple of hundred different coins from different countries - probably all worthless, but I figure I might be a grandparent sometime sooner or later, and having a tin of weird old coins seems like the sort of thing to do.
Somehow, I got 5 rubles that were mistaken for a quarter in my change at some point recently. Only figured it out when the coin wouldn’t be accepted by a vending machine. Looking up the stats, it’s 25mm and 6.45g, so reasonably close to the US quarter.
I was given a 1918 florin in place of a 10p coin - a few mm wider but twice the weight, and 92.5% silver.
Well. Proves me wrong. I guess I’m just used to them, because it’s not a mistake I could easily make.
Not quite what the OP is looking for but still a coin story.
In 1976 I was stationed in South Korea, with the US Army. At the time there was a Korean coing, silver colored, the 100 won coin. Won to the dollar was 481 won to one US dollar, so the coin was worth 20.8 US cents. It was so close to the quarter in size we would try to us it in vending machines in place of the quarter. It would often work, but sometimes it didn’t and would gum up the machine.
So you won some, you lost some?
Not in change but we were living in the Czech Republic and on holiday in Croatia when my wife found a 10Kc Czech coin on a beach.
Looked at some change I got today, and one of the nickels was darker than normal. It was a 1945-D WWII “nickel” made of silver (with the large D above the dome), in VG condition. Score!
I got a two-headed dime once - the vending machine kept on rejecting it, making me look at it more closely. Obviously a magician’s coin.
About the same time (ten years ago) I got a 1970-D quarter but one that was the thickness of a dime stock. Again, the vending machine rejected it several times, which made me look at it more closely; I went to the lab and got a micrometer and put it on a scale to verify it was dime-thickness. I hadn’t heard of it before, but it’s not uncommon.
I got a krone at a Dollar General Store in Arkansas.
5 dinars Serbian … various euro coins … 10 roubles Russian, this week.
The other day as I was leaving the store I thought something felt a little heavy in my pocket. I checked and discovered that I’d gotten some Yapese rai in my change.
I got a nickel the other day that was minted proof and somehow got into circulation. I’ll have to check on the date…
A lot of US coins, some West Indian coins, and recently a Lebanese 500 livres coin (about the size of a quarter and worth about 40 cents Canadian). I also have received a 20-cent Newfoundland piece with Queen Victoria on the face (clearly pre-1901 but the date is too worn to make out), and a variety of old Canadian coins from the reigns of Victoria, Edward VII, and George V. I make almost all payments by debit these days, so I don’t get a lot of change any more.
I’m not sure what’s rarer - the 1940 dime or a pay phone. 
The old 10p was identical in size and weight to the florin (the old 5p was the same as the shilling) - prior to the 10p being sized down in 1993, there were lots of florins still in circulation as 10 pence pieces.
I was looking through the change in my pocket as I walked into a hobby store. Found an old but not rare nickel…
…so I found a coin collector’s album for Jefferson Nickels, and clicked the nickel into the slot for whatever year/mint it was.
Some kid’s going to find he has a head start on his collection.