Most of the co-ops I have encountered allow you to pre-order large quantities of bulk bin items at wholesale or just above wholesale price. Granted, this means you may end up buying a 50lb sack of flour or couscous at any one time, so this isn't viable for those who live within a small household community. However, if you have a large family and go through tons (literally) of dry goods each year, this could be big savings. If you combine this with the member discount (hours of work in exchange for a discount), it's even better.

Also, something I don't read about very often is eating common plants that are indeed edible, just not commonly eaten in our society. I'm not sure you would save much money doing this, but it might make for a fun experiment in frugality. Some examples are rose petals / rose hips (organic/untreated only!), acorns, young dandelion leaves/flowers, miner's lettuce or sea vegetables. I definitely wouldn't do this without some sort of guidance- get a book or a knowledgable friend- but its really most often the herbicides and pesticides used commercially that are most dentrimental, and not the plants themselves.