acho que não

The replicator, no doubt. Inventing the replicator, assuming it's cheap and readily available, would basically eliminate need, would turn the worlds' economies on their ear, and hopefully go a long way toward bringing about the utopia that Roddenberry envisioned.

If I were being extra-geeky, I'd point out that in Treknology, the transporter and the replicator are related, but I can't remember exactly how, so I guess I'm just regular-geeky.

The transporter, because then I could transport to the places I wanted to eat or visit. Plus it has that wonderful sparking effect and sound.