Where are those firemen when you need 'em?
IMO I would be attempting a rescue. You aren't sure if the food has been eaten by this cat or a 'coon. If a 'coon then kitty is going to be in trouble very very soon. No food or water for that long of a time is deadly to a cat.
Does the cat belong to someone?
Is the shed flat roofed? If so you could also try to set a live trap on top of the shed if kitty doesn't come down by tonight. That way kitty is safe and can be taken to the shelter at the same time.
Good luck. Let us know what happens.