Hey Panda's Pick One Fictional Item From Any Universe And You Can Have It, But The Person Who Own's It Can Come After You.

I would take a Harry Potter wand or a jabber worm, either could be very useful, or maybe a bag of holding which would be even better. the wand for Accio, the jabber worm to understand everyone, and the bag of holding simply for the basic utility of being able to carry it all around everywhere