Drink coasters are a crowded market, populated by people trying to get rid of off-cuts or new designers desperately trying to make a thing they can sell. You rarely see anything clever. But British homeware company Mustard has come up with a decent idea for one that should sell like hotcakes amongst the target market.
All the Instant Coaster is, is a piece of tempered glass with a slot in it, that perfectly fits a Polaroid photo.
The copyright-savvy company is careful not to use the word "Polaroid" anywhere in their copy, but the graphic elements in the package design make the connection clear.
In any case, this is the simplest way I've seen to mass produce a "personalized" coaster.