Uhhhh. Probably the fridge. Maybe the microwave/oven combi, but the microwave no longer works so it's a bit less useful. If you purely look at the basics of survival then those would probably do it. Maybe the heaters, because surviving in a cold room is also pretty shit.
You could also argue that the smartphone I'm typing this on or the laptop are the most useful. It really comes down to semantics of "useful".
"De Grote Zaal" by Jacoba van Velde. For school we had to read many books. In the earlier years this could be anything as long as it was Dutch, so translated versions of English books were fine. I could read stuff like Harry Potter, Lord of the Rings, etc. However, at some point the requirements shifted, and we were only allowed to read Dutch (non-translated) works of literature. This shit single-handedly killed all my fun in reading. Dry books about old people or about the war.
"De Grote Zaal" is the one that I remember the most. It's a short book, but it goes pretty much nowhere and doesn't at all speak to the imagination of a teen guy. To me it represents the death of reading as a hobby. I've tried to pick up reading again, but it has since been replaced by other things and I just don't make the time for it anymore.