Depends.
If we're talking something that the duration of can be pretty much figured out? Fine. I'll share, as long as I don't end up short.
If we're talking a major type thing, AKA katrina: If you haven't seen any progress inside of about a week, you best figure it may be a long time before help arrives. Then I've got enough to help folks with with the essentials.
If we're talking something as rough as a nuke strike or similar:
IF I lived through whatever it was, assuming that the National Guard, etc., are going to be tied up on matters regarding keeping us intact as a nation, rather than worrying about civilian losses here and there, mine means MINE(this includes immediate family), and all bets are off.
A basic guideline: Katrina and similar things, such as the recent winter storm up north are a state or regional thing. The rest of the nation will be able to assist. Mobilization may take a little time, but help will come within a month at the most usually.
Something that is devistating to the entire country? Best hang on folks, 'cuase everyone else will be worrying about #1(and that isn't you).