The best thing that you can do to not lose something is to not bring it in the first place! However, when traveling we do have to bring some things and since we can't go something with absolutely nothing, here are my top tips.

Establish a ritual

Everytime you leave a place, and I do mean every time, check to be sure you have what you brought. I check 3 essentials: my phone, my wallet, and my passport (if I'm traveling abroad).

Anything else, I can replace fairly easily, but it's whole different ballgame as soon as you lose your phone and ID. At least you'll be able to get home! 

This habit seems like a lot to do. Trust me though, it's way easier and takes less time and stress than if you actually leave something.