Hanging your food in a plastic or nylon bag still leaves it vulnerable to birds. So I was told by a G.C. ranger.

The last time I backpacked in the Grand Canyon I bought a Ratsack directly from the permit office. The Village store sells them too, at least they did last April.

The medium size easily held 3+ day's worth of food. It's not the cheapest or lightest solution but I felt very confident when leaving my food unattended and while sleeping.

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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.