I mostly don't shop overseas for pleasure. I don't want to spend my time on that, I make bad purchasing decisions on the go, and our currency is very weak against foreign currency, so things are always more expensive than they are at home.
That said, there are some occasions where I definitely had to buy something out of necessity. Embarrasingly, the more I think about it the more occasions I come up with. Mostly, because I am light packer, I err on the side of leave, rather than pack unless I am traveling by car and I misjudge the weather. Fortunately, all these things have earned their keep in my closet.
Once, I was about to embark on a cruise, and I broke my sunglasses - I think I sat on them. Needless to say, they needed to be replaced.
Another time, we traveled to Bordeaux and Paris. What worked in Bordeaux, didn't work at all in Paris, the latter was much much colder. I had to buy a blazer. I wore it a lot afterwards, will keep wearing it again this spring. My hubby forgot to bring a tie, and we had to look for a department store to buy him a decent tie, and a windbreaker, too.
One time, we went to Amsterdam. Again, underestimated how cold it would be. I had to buy a winter scarf and a matching hat from H&M in Amsterdam. Still wear them. I also got a lovely tote bag from the street market, but that was for pleasure.
Hah, I just remembered one more thing. In Vegas, I had to buy a pair of flip flops, because I was incredibly uncomfortable in my dressy pointy-toe flats, even though they were normally ok. I guess I just couldn't anticipate how much walking we would do in Vegas. The cashier at CVS(?) joked that she sees that multiple times every night.
Last summer, we had to buy a towel for the kiddo at an amusement park.
Hahaha, this list is getting too long