Consider using only one hand to stuff the cash into your pockets. The robbery will take a little longer, but if the alternative is setting your gun down on the counter, it's worth the extra time.
As the surveillance video of the incident shows, some convenience-store clerks may be so rude as to grab the gun and turn it around to point at you. This is a severe breach of robbery etiquette, but should it happen your only options are probably surrender or flight. The worst choice is probably what this gentleman did, which was to first flee, then rush back into the store to try to take the gun back from the now-heavily-armed victim. Not only are you unlikely to get the gun back, the commotion may give someone time to write down your license-plate number.
Neither man was injured during the incident. The robber was tracked down in a nearby apartment and arrested.
Link: CBS News