I'd ask for a gadget-making gadget. Sort of like a Coke machine, except gadget-dispensing and programmable so that I could make my time-pausing devise, or my dimension-seeing device, or a really nice stereo, as needed.
Wish I'd thought of this. This would in fact be the gadget that I would most want.
The first thing I'd get from it would likely be a mind reader device, to be able to see what everyone around me was thinking.
The gadget I really want is the time-stopping device that has already been mentioned by a few people.
But in the interest of not being repetitive, my second choice is a pair of X ray glasses that will let me see whether a woman is attracted to me or not. The glasses would make the woman glow with a colored aura. It would be like the terrorism alert...green is she has no interest, yellow is that she's rather indifferent, orange is that she's interested, and red means she wants to jump my bones.
Not incidentally, if I could replicate those glasses I'd be rich enough to make Bill Gates look homeless.
Not really a gadget, but I wish I had my own collective. Kinda like the borg, but it would just be me. My clones. I could do multiple things at once and be in multiple places at once and best of all I'd be a collective consciousness. Actually they don't have to be clones as long as I was the consciousness.
That'd be like a major boost for my creativity, something I kinda need right now.
An instant teleportation device that could take me wherever I want to go because I really want to travel but costs get in my way. With a teleportation device, I could go to places like Egypt, the Amazon, or the Outback & be back for dinner!
I kinda wish I had The Button - the one which launches all the nukes at whatever it is they're pointed at and ends the world. I doubt I'd ever push it. But every day I would feel that I was contributing something valuable to the lives of every person on the planet by not pushing it.