Truer advice has never been spoken! Well... except for the last, ahem, couple of decades here...
A few very minor points:
Pick up a good, large, black, folder with a pocket clip so you don't have to dig it out of the bottom of your pocket if needed. Also, put it in the pocket OPPOSITE your gun side. You might be a "righty", but learn to draw it and use it with your left hand. Why? Because you want to keep your strong hand free for your gun
While holding less rounds overall, consider a .40 such as the Glock 22 (equal to the G17, holds 15 rounds of .40 per mag instead of 17 rounds of 9mm... also think of H&K, Sig, or S&W... the S&W Sigma series was designed in conjunction with Glock... Sig is a great firearm and made in NH... H&K is another example of fine German engineering... There's also the Beretta.) While having a nice high-capacity firearm is the best for any of the situations described, also consider some of the compacts. Instead of the G22 look into the G23 or G27... Instead of the H&K USP look into the USP-C... Instead of the Sig P229 look into the P239... etc. Why? read on...
The smaller firearm you will
carry is move valuable than the brick you leave at home! If it's the best for you consider getting a pretty small S&W J-Frame revolver with a couple of extra speed loaders. Sure, it only holds 5 rounds, but once the group hears the bang and sees some people bleeding and screaming, you'll have time to reload (just have to practice doing so quickly with a revolver)! Regardless, you're better off with that little 5-shots of .38 (even if you don't carry extra speed loaders) that is easy to carry than leaving something bulkier at home! Besides, some of the new little firearms can easily fit in the palm of your hand... from the J-frame to the Kahr to the mini-Glocks... and holsters are available for them all! Even if you're wearing shorts in the summer, you can carry one of them. Chose the largest caliber that you can comfortably
fire and carry! Bigger bullets make bigger bangs and bigger holes! 'nuf said. (While I, personally, consider them almost useless for personal defense, if you feel the need move down to the .380, .32, or even the .25 or .22... just remember that smaller caliber is less noise to scare the assailant and does less damage. BUT... people have died from a single .22 caliber shot. It's just like Real Estate... location, location, location!)
Finally, whatever someone choses to carry... practice, practice, practice! Get proficient with that carry weapon. Your life and the life of your loved ones may very well depend on it.
I suspect as the economy gets worse and things get more desperate across the nation we'll see more of these incidents... just look to Greece and Spain now... coming to a neighborhood near you. (Hopefully not, but I don't feel very optimistic.