I can see the worth. If its a tsunami you're trying to survive, it'll be over in a less time than for you to run out of air. The five days of food is once the waters retreated and you have to wait until help arrives.
Unless it takes you out to sea... Then you're fucked.
Basically it's that capsule thing Bond had in one of the movies. All you need is Her Majesty's Armed Forces to come to your aid before the champagne and caviar runs out.
if it's airtight, how do you breathe?