Storage containers will make a large difference in the successful exclusion of bugs and rodents. These pests can quickly gain access to food packaged in paper or plastic bags. Large airtight food-grade storage buckets can help eliminate the problem. I purchase many of my food storage items in large metal cans. I live in a dry climate, so I have not had any trouble with moisture or rust.
Most items purchased in metals cans have an oxidizer packet in the can to help retain quality.
While purchasing food in these containers may be more expensive to begin with, the storage success may make up for the price difference. If I have a choice between powdered milk in a box, or powdered milk in a metal can, I choose the can. Flour is an item that is suseptible to insects, and does not store well over long lengths of time. For this reason, many people store wheat, and keep a wheat grinder on hand to grind their own flour in time of need. I have successfully kept flour in my cupboard in airtight containers for a year or more, and I have had success storing it in large airtight plastic buckets as well.