I would second the Vittles Vault if you are going for large amounts. I use them for dog food. The lid is exactly like a Gamma Seal, and it is easy to use and holds up well.

If you want to use regular 5 gallon buckets, you can get a food-grade version from beprepared.com and also Gamma Seal lids to make them much more convenient for everyday use. $13 for one set.