The over the shoulder style bags are really best suited as a GHB, Get Home Bag. It's a bag that's designed to get you through the first 24 hours. My man purse, aka 'Murse' is a Maxpedition Jumbo Versapack. I've had it for a couple of years now. It's set up as a GHB right now and it's got a bit of extra room for stuff. Anyway right now it has the following in it.

A full MRE
A couple of power Bars
A couple packs of snacks
32 ounce Nalgene bottle
Stainless Steel bottle cup
Titanium Spork
Maps of Florida and Jacksonville
Can of Mace
Multitool
Pocket knife
Bic Lighter
First Aid Kit
Ben's Max 100% Deet
Surefire SC1 Spares Carrier
Surefire E1L light
Whistle
Earplugs
Cell phone
PDA
Green Shemagh
Buzz Off bandanna
Water Proof notepad
4 Sigsauer 229 9mm magazines

I'm looking at some of those bags on county comm. My wife just got her CCW and went with a .357 magnum revolver. So I'm looking at getting her one of those bags in case of car troubles.