The stuff described would mostly fit in a backpack as it's all backpacking gear to begin with. The only thing that wouldn't would be 30 days of food and water which is probably overkill. A reasonable food supply would fit in a couple cubic feet and multiple redundant water purification options could fit in a pocket.

I'm just a backpacker though not a doomsday prepper, the stuff we carry isn't always appropriate for an emergency situation and is generally geared towards being very portable rather than robust/100% reliable.