Here is a true story. When I was 18, I had a job for a large tractor trailer repair shop in Jackson Michigan. I used to drive a truck to Detroit/Dearborn/Willow Run area three times a week to pick up parts for long haulers who were broken down. On one particular occasion (remember this is before cell phones and GPS), I was in a very bad area of town, trying to find my way to some salvage yard I'd never visited before.
While at a stop sign I'm looking at my map to try to figure out where the heck I am when some crack-head puts a loaded revolver to my head through my open window (no A/C). For those heroes out there, even if I had a gun- even in my hand, when a desperate person puts a gun an inch away from your head and screams "Get the f*** out of the truck"- you get out. Period. I left the truck out the passenger side and stood there while he drove away. I didn't give a shit about the truck or the 6-71 Detroit Diesel I'd picked up earlier loaded in the back.
A strange calm came over me as I looked around at the most forbidding surroundings you can imagine in a bad area of Detroit (murder capitol of the US at that time). No pay phones. No nothing. I started walking and to my surprise a police unit came by about a minute later with lights and sirens on. I flagged him down and he went right past me. That's when I started to get really concerned. Shortly after that, another unit came by and stopped. They loaded me in the back and took me to a station a couple miles away. On the way, I gave them my story and they told me that guy had stolen (they didn't call it car-jacking then) another car before mine and shot the driver. Lots more to this story, but the moral is- even if you have a gun somewhere and think you're going to fight back, forget it, you're not. Second, give the friggin' car up. Anyone desperate enough to carjack you with a weapon is NOT the person with whom you want to discuss the matter. Third, imagine if when he tried to flee in the truck it was stuck in Park. Where do you think his frustration would have been aimed?