Rationing food is one of the worst things you can do. If you eat less than your body needs each day your body will begin burning fat but won't do so in a proper 'fasting' mode and you'll last way less than 40 days...and you'll always feel hungry and miserable. You should eat the food you have early and use that energy to build a good shelter and collect a boat load of firewood...then relax and conserve energy while waiting to signal that plane or boat. If you expect to be out longer than 40 days, then the whole scenario changes.

The information I have on this comes from the courses I've taken at the Boreal Institute. There is also a fantastic book about this kind of information but I forget the name...I'll post it when I get home.