If you are driving to the location, it may be more adviseable to dress lower-profile and have the gear in a lower-profile bag that you can put between the seats or whatever. Driving 90 miles while wearing a tac-vest or chest rig is a very good way to NOT blend in; you might as well wear a big "Follow Me and See Where I Keep the Rest of My Stuff" sign. And if you're
not wearing it in the vehicle, then your stuff will be more accessible from a well organized bag than from a vest or chest rig folded up on the floor.
Here's one option, from OST:
It is designed to be carried comfortably over the shoulder (strap goes to opposite shoulder for no-hands security, of course), includes mag pouches and a dump pouch, and I believe it can be configured with internal pistol holster/mag pouches, etc. (if not that one then other ones definitely can).
More options here, including some discreet rifle cases:
http://www.onesourcetactical.com/index.asp?PageAction=VIEWCATS&Category=241
In a Katrina type event, bringing unwanted attention down on yourself, whether it be from criminals or out-of-town authorities, can be a big negative.
In my opinion, chest rigs and tac-vests are great if you need a way to carry your stuff around in isolated areas or on your own property (assuming high vs. low profile isn't an issue), but for an emergency evacuation I think the low-profile choices have a lot of advantages.