I disagree with this - the 72 hour kit is your get home or wherever your plan to go is bag. the pantry is your cache or stash.
One cannot determine the amount of time it will take to get home, or if that is even feasible. The reason 3 days has been chosen as the magic number is because it has been determined that that is the ideal amount of gear that an average person can carry and still be mobile.
Think of it this way, my long range patrol pack weighed in at 110lbs and was good for 7 to 10 days, the avg 3 day patrol pack was 40-50 lbs. The 3 day pack can be stretch to twice that time, but thats pushing it without scavenging.
So plan accordingly and think of it as solving as much of the what if you can, while staying withing the 40 lb range.