You'd be surprised how much room you can come up with if you try.
Store water containers under beds, can goods in closets, etc.
Another good way to store water is in a waterbed. There is a problem with some waterbed chemicals, however.
Some landlords specifically prohibit waterbeds, for good reason. There is a lot of room under regular beds though, but my kids used them to hide dirty dishes and socks ;-)
I like the 72 hr trash can idea. Plus we have basic camping equipment. More can be picked up at yard sales. I've done a lot of camping in the past, so I know what works, and I'm interested in what's new.