I like Datrex too, its easier to use, since it is subdivided into individually wrapped 200 calories bars within the 2400 or the 3600 calories vacuum overwraps. I keep three 2400 cal bars in my kit for 2 people, which should last us as much as 4-5 days.
One is mostly limited by water in a survival situation anyway, but food is good to have around. <img src="/images/graemlins/cool.gif" alt="" />