Re: Welcome to McGuffins. May I take your order?
Aladdin's lamp and ring. Particularly if you go to the original idea, which had none of this "three wishes" bumf, and w/o the "twist the wish around" stuff. The genie of the lamp (and the genie of the ring) obeyed the owner, fully and willingly and helpfully, *and* with all their considerable power.
Then there's "The Gizmo". In it's "off" form it's a unremarkable medallion. When turned on, it turns into whatever non-magical/non-superpowered/etc. device you need, and changes back into a medallion when you no longer need whatever it was. Important note: that's *need*, not want; and, it's a bit peculiar in deciding what you need.