"Everything you've got" really was an accurate description of what was needed.

The local people knew even before Katrina hit that they didn't have the resources to handle a storm of that magnitude. That's why they asked for assistance. The plan did not include evacuating everyone out of the city. They knew they didn't have the resources for that (Mayor Nagin said precisely that a couple of months before Katrina hit). The plan was to evacuate as many people as they could to shelters using municipal busses. And that's exactly what they did.