Photo by Sven Kleinschmidt https://pixabay.com/en/users/sirigel-396082/
While queueing at airports or waiting for buses etc. always keep a hand on your luggage or were you have a few bags keep your foot on the handle or a strap of the extra bag.
The smallest resistance is often enough to stop a bag being snatched especially if its heavy but remember if they seem intent on having having it (you feel threatened) just give them the bag, things can be replaced but you can't. :)