What will you do? What WILL you do?
If you're smarter than the dude (I know, not much of a challenge) you feed him the bills from the cash register a few at a time until he has a wad of cash and is getting impatient. When he takes his hand off the shotgun (remember, it's laying across the counter) to stuff the cash in his pock you grab the shotgun quick-like-a-bunny and turn it on him.
Watch him run out the door, even quicker than a bunny!!
But wait, there's more.
After a few moments, he stops to consider.
Hey, that guy has my shotgun. What am I going to do for a gun tomorrow night, when I hit the 7/11 across town?
So he barges back into the store, leaps over the counter and starts to wrestle you for the shotgun.
Here's a tip: Pull the trigger.
Yep. That works.
See the video.