My dad passed not too long ago, and out of his estate I got his little collection of KLM Delft Blue Houses. They are little miniatures that hold Bols liquor that are awarded to first/business class passengers on KLM overseas flights.
Nowadays a new house is issued annually on October 7th. There are 104 total at the moment.
My pop had 21 of them, none from a flight, all picked up in thrift shops.
There is an interesting official collectors App that catalogs all of the houses.
My broad observation is that they are really neat little collectibles. Basically all of them represent a real house/building in the Netherlands that has some sort of interesting history.
A handful of them are worth a lot of money, but most are $15 to $30 in the aftermarket (or two bucks in a thrift store).
Not much else to say, except if you're traveling to the Netherlands, keep your eyes peeled in flea markets and second hand stores. They are fun little collectible souvenirs, decoratively good looking when you get a little row of them going (they're all scaled so that they nicely align as row houses next to one another), limited enough that they lightly appreciate and value over time, fun, accessible history tied to each one.
Pretty neat - I'm glad I inherited a little horde of them. Not worth a lot, but cute, interesting, and tied to a country that I really like visiting :)