Scepter makes good cans - 2.5 and 5 gal, available at various places, such as:
http://www.brigadeqm.com/store/qsearch/search.aspx?query=scepter

You can also buy "imitation" scepters, for $19 (though apparently they work fairly well) at LC Industries.
https://www.redcheetah.com/lci/index.php (log in under "guest", then search "water can." There's lots of items, but you can skim the thumbnails and find the 5-gal types)

Finally, you can just go get the typical 2.5 or 5 gallon water jugs that companies deliver to your house. Many grocery stores, or Lowe's, sell them. Supposedly they're good for several years.

Personally, I have about 10 gallons in store containers (a few 1-gal, a few 2.5 gal, and a few pallets of 20oz bottles) in the house. My garage also has 2 5-gal scepter cans that I just bought, with the idea that I fill them as events evolve. Being on the east coast, I anticipate either winter storm or hurricanes as my biggest events, both of which typically have some warning. The pre-packed is more of a catastrophic, no-warning storage.