Imagine this scenario.. it could very well happen.

[Hot brass]

let the robbery take place as long as no one gets hurt. I bg hurts someone or threatens me and or mine its shtf time. I will do what I am forced to do.

 

[TheeBadOne]

Much would depend on how I was armed. If it was my tiny but eminently effective Kahr MK-9 I might draw and secrete it (under arm/arm pit/pocket/magazine-newspaper, what ever I had) to be readibly assessible if the BG began to fire or began to threaten me. I would seek cover and not do a thing until he left (being the best eyewitness I could be). If I had my cell phone with I would dial 911 as soon as he left. If conditions were right I would dial 911 right away, whisper "armed robbery/name-address of said store. This would almost never happen as it would cause a harsh reaction from the BG if seen.

 

[444]

"While everyone else in the store was distracted I would fill my pockets with Hostess fruit pies and then slip out the back."

Why not do everyone concerned a favor and before you slip out the back door yell, "Twinkie the Kid, HELP !!!!!"

 

[WvaBill]

Paul White was to the point with a measured, flexible response.
This scenario doesn't give me near as many heeby jeebies as the one in which I am out with family. We are in an eatery and bg comes in with only the intent to off as many with his weapon of choice.
My response will likely end in serious injury or demise, but given lack of cover in restaurants and the unlikely process of keeping three under 7 children quiet, I would probably use movement, cover, and concealment to draw fire from family until/even if/ I could srop reacting and bring the threart to bg.

I just never was so optimistic in my imagined confrontations.