Let's say humans invented a time machine which will transport you back in time. And can only be used once, and there's no getting back. Assuming you have volunteered or was forced to go.
So what item would you bring to save your @ss from being tortured by barbarians, turned into a meatsoup by cannibals, or swallowed by Dinosaurs?
Before you comment, you might as well provide which time period you are choosing. (e.g. Jurassic periods, Medieval, Renaissance, Biblical periods, World War 2, etc...)