I agree that if the authorities say to evacuate your best bet and best odds for survival are to evacuate. That said, as always, the final analysis and decision, and responsibility, has to be left to the individual.

Reading a bit about NOLA one source claimed that about approximately 10% of the population didn't evacuate. Some didn't hear the call. There will always be some who don't. And there were some number who couldn't or wouldn't leave. The same source claimed that 90% compliance is about as good as it gets and that this is what can be expected from any average American city.

The sooner you leave the better. Most of the horror stories associated with the evacuation process, gridlocked vehicles running out of gas while the occupants suffer the heat, hunger and dehydration, were a result of everyone waiting until the last minute. The people who left a few hours earlier found the process much less harrowing.

On the nuts-and-bolts question of provision for such disasters. Retreating into the attic is one way to get above the water. A problem in NOLA was that once in the attic there was no provision for getting out. Some people resorted to laying down in the attic space and kicking their way through the roof deck. Fine enough if your strong enough, you have time, and the deck is relatively weak. A easier and more reliable solution would be to have a few tools pre-positioned in the attic beforehand. Something as simple as a small axe, hatchet and perhaps a pry bar might serve you well. Trapped in an attic these tools would give you the mechanical advantage needed to get through the roof deck quickly.

An even better solution is seen in many older houses in Europe. They have a hatch built into the roof that allows transit from the attic space out onto the roof. This combined with hatch in the ceiling and a ladder or built-in stairs gets you from the house interior into the attic space. This would be arranged so it could be locked from the inside so security isn't compromised. This has the added advantage in normal times of allowing easy and relatively safe access to the roof without resort to a ladder on the exterior.

Reading about such innovations I also found out that in some Dutch houses a small flat-bottomed boat, one light and small enough to be deployed by a single person of average strength,is stored in the attic. This is placed in the attic and put into service by way of a gable-end on the roof that has a hatch or some portion designed to be easily removed. Quickly kicked out if need be.

I would include vital related equipment like oars and perhaps a push-pole. I would tie a stout line from the bow to a sturdy point of attachment in the attic with sufficient slack to allow the boat to reach the water. It wouldn't do to have your boat drift away before you get into it. With it tied a standard sailors solution is to lash a sturdy knife near where the line attaches to the boat so you have some way of releasing the boat quickly if a knot jams or it is too cold to use your fingers.

A simple aluminum ladder sufficiently long to go from the gable end of the attic space and the top of the roof would add some additional options.

I would be tempted to add some basic and rugged tools like a decent knife and some rope but would hold off on the more delicate supplies like food and medicines simply because attics tend to be hot and otherwise lousy places to store such things.

A cheap aluminum John boat with oars and a ladder could stay in an attic for decades without degrading much.

There was some mention of roll-up emergency ladders. Those are fine, far better than nothing, in a pinch but they tend to be miserable affairs compared to even the cheapest regular ladders if the regular ladder is tied off at the top and made so it is incapable of collapsing if any mechanism fails in the heat of the moment. On the job I lash the rungs of the two sections of a extension ladder together in case the regular locking mechanism fails. That has saved me more than once.

I would expect to evacuate if advised to do so. But if I chose not to, or if the flooding was too rapid then staying ahead of the water by dragging my BOB up into the attic and from there up onto the roof, ideally with a boat and/or ladder ready to go, would give me a fighting chance.