Of course the most important items a bag checker would be searching for would be a bomb or a gun. Fact is the odds of discovering an offensive weapon such as those are minimal.
What most bag checkers will encounter are the everyday prohibited items like those above.
The pictured items are not the only items that are discoverable. Prohibited items are whatever a venue deems to be prohibited. It may include food, cans, laser pointers, noise makers or any number of other items.
Large bags or backpacks can be dark inside.
Without any light it is difficult to see the items inside the bag.
Using a flash-probe illuminates the inside for better visibility. The probe allows for items to be moved around. The probe also prevents the need for the bag checker to put a hand inside the bag. This could prevent injury on a sharp object or a deadly poke from an uncapped needle.