Two years ago while camping in the Zion Narrows, I stored my food overnight in a heavy vinyl dry sack I normally use for kayaking. We slept out, no tent. The food bag was right next to my head where I was sure, I thought, I could ward off any small critters.

I slept very soundly that night. Too soundly. I woke up only to find a nickel sized hole neatly chewed right through the bottom of the bag. Food had been eaten by some bold, unknown creature.

I'm not sure if an Ursack is the answer. Quoted directly from their site:

"Is Ursack resistant to rodents, marmots, wolves, etc?
Ursack is highly effective against Marmots and raccoons. It should not be considered wolf or dog resistant. That's because they have sharp teeth and strong jaws. Bears have great strength, but their teeth are not sharp.
Other rodents have varying degrees of success. Sometimes mice can chew very small holes, but very little of your food is likely to be taken. Some species of squirrels and (we have heard) pine martens have greater success, and may on rare occasion chew holes in Ursack."

Certainly a bear cannister is the most bombproof solution but they are heavy and expensive.

Hanging works great against earthbound critters but there are some very smart and aggressive birds out there too.

I too have toyed with the 1 gal. paint can idea. Almost bought one at Home Depot. But they're not as light as I'd like and they require some sort of tool to open.

The Ratsack is another possibility. I'm considering one for my upcoming Grand Canyon jaunt since some of the back country food storage containers (i.e. ammo cans) have been removed by the rangers.

I think a metal cookie tin of the right size may work too. I just have to find one. Thin metal IMO is better than thick plastic for this application. Better against sharp teeth and lighter if it's thin enough.