Food banks get their donations from 3 primary sources: the government, the private sector (which includes both individuals and corporations) and crop subsidies. Government sources and crop subsidies are both down - the former because of policies and the latter from a combination of crop failure and farms growing crops for ethanol rather than food. Donations from the private sector are way down too, because in this crappy economy people are too worried about paying for their own food (and gas) to feel comfortable giving funds or food away. Further, the upheavals on Wall Street are causing a distinct lack of corporate donors to these charities...not just because of the companies directly affected, but also all the companies who had investments in directly affected companies.
In short, the charities that are there to help out hurricane victims are themselves hurting. If you've got spare funds or food to give, please consider it. Cherie Priest has a good list of charities here: http://www.cheriepriest.com/2008/09/1