So, then I thought that of all technogies, I would like best to have a door that opened in several different places, like in Howl's Moving Castle, so that I could have a door that opened in Iceland, near Husavik, or on an uninhabited Scilly Isle, or in Istanbul (I liked Istanbul a lot, but I found it stressful as a place to spend much time. It would be nice to be able to just pop there for a wander, a shop, coffee and pastries, then come home).
Then I thought that I would like to own a pleasant pocket universe, like the ones in several of Diana Wynne Jones's books, and the ability to zap people into it, so that when afflicted by people who were grumpy, annoying, warlike, loud, or simply in the way, I could zap them safely away to a pocket universe where they would be quite safe but where nobody would have to deal with them.
Then it occurred to me that maybe I should simply go and live in the pocket universe myself. An attractive idea, if a little lonely perhaps. It does lack the charm of being able to point at someone and go 'zap' and have them painlessly vanish, which sometimes seems like it would be THE BEST THING ever.
But at the moment, I think if all the treasure of gadgets and devices of fiction were laid out in front of me, I would probably grab the Time Turner, out of the Harry Potter universe. Because what could be better than just being able to have extra time, whenever you wanted it? It would be a bit like that episode of Stargate where everyone gets trapped in a temporal loop but nobody can remember the looping apart from Teal'c and Jack O'Neill, and they learn to throw pots, and play golf. Not that I have any desire to play golf, but you know what I mean. You could just randomly have a nap, or spend two hours painting or gardening or going to the seaside!