We're still working on our apartment-sized earthquake survival kit.
Aside from ensuring the happy survival of our household, we're driven by the need to put together one that's compact.
So we've been trying to figure out how to deal with storing the requisite amount of water: a minimum of a gallon of water per person for 3 days.
For us, that means about 10 gallons, or ~1.4 cubic feet of water that we need to keep readily accessible in our cramped quarters so that we can find them quickly in an emergency. That's about 1.4 cubic feet of space... assuming we use Aqua Blox, which are durable, stackable and spill-proof.
We're also intrigued by Target's $29.99 Reliance Emergency Essentials Kit, a water-oriented emergency kit that includes water treatment tablets, water containers, and a "Luggable Loo" portable toilet.
We're not sure whether it's actually advisable to replace those gallons with the equivalent amount of water purification supplies, and the toilet is probably an unnecessary luxury. Perhaps the whole thing could be condensed to just water purification pills and collapsible water containers.