The simple "churchkey" bottle opener exemplifies invaluablism. These ubiquitous and inexpensive little tools are extremely dear when you need one. In other words: "invaluable".
The popularity of craft brewing has driven continued relevance of this classic tool. You will not find many twist-off caps in the micro-brew aisle. Most craft brewers use traditional bottle crowns to cap their beers, requiring some sort of tool to open them easily. Contemporary beer drinkers need these decidedly old-fashioned tools.
Save your churchkeys; they may be endangered. Because of the inexpensive nature of this simple tool, variations on the theme are numerous. Give-away marketing versions abound in many different forms. Consequently, paying for one almost seems silly. But try finding the old-school churchkey article for free and you will quickly find that this style is out of fashion. And, as described below, one-half of its raison d'être ("can tapping") is today passée. For anyone seeking churchkey verisimilitude, at home or maybe for a proudly invaluablist short term rental, see the nearby aside for links to buy new versions of this old staple.
The churchkey features two primary functions; removing bottle caps and "can tapping". But with most canned beer featuring pull tabs today, or other clever quick-opening mechanisms, can tappers are not called upon by beer drinkers anymore. Meanwhile, motor oil, another staple canned product necessitating a can tapper, mostly now comes in plastic bottles that don't require can tappers either. The dual-purpose churchkey is holding on to relevance, but just barely.