When traveling, I normally carry along with me my phone, some snacks and money. Depending on the length of the journey, I can carry along my laptop so that I can can do my research while traveling.
Alright, maybe I misread what you were trying to say because I definitely believe that one's smartphone is one of the major items someone get the moment you plan on traveling. It's offer lots of functions that someone can't do without in course of a journey.
The first thing that came into my mind is my smartphone. This is very essential next to money and passport. Whenever I travel, I always take pictures because this serves as my memory of that vacation in a certain place.
I think clothes and medicine top the chart for me. If I have that then I am ready to go. You can then count the camera and the food on the next in the list. You can also add the other additional items into this. You can make some good list out of it. And then decide what may or may not work in such case. I think depending on the purpose of travel things can surely change.