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”.