Well, there's a few, creative ways to do that.

ie, instead of a bed frame, stack canned goods under your box spring.

For water, get Water Bricks, and use them instead of milk crates to build shelving.

Just some ideas.

That said, 72 hrs is like a week of groceries per person, and 14 gallons per person. 14 gallons of water per person sounds like a lot, but you can get creative there with the water carboys stored in "shelving" that supports your TV, for example. Or, Water Bricks like I suggested before.