As I shop for items on my three-month supply list, I always find myself with the dilemma of whether or not to buy in bulk. Typically buying in bulk will save money. But you have to be smart about it -- if you don't know comparison prices, you might find yourself unwittingly spending more. It's easy to just assume bulk store prices are lower, when in fact they are similar or even more. With a little searching on the internet, you can usually get an idea of what a good price per ounce/pound is.
I also have to remember to pay attention to the container sizes. It doesn't do me any good to save a bunch of money by buying a gallon of mayonnaise, only to have it go bad before we've used half of it. With mayonnaise, for example, I try to find the best price on the smallest possible container. Some bulk items come in large package sizes, but can be redistributed to make smaller servings and reduce waste. I do this with ground beef and shredded cheese (neither item is on my three-month supply list) that I buy at a bulk store. I just repackage into smaller containers before I put them into my freezer.
If you plan your three-month menu trying not to rely on refrigeration like I am, then you also have to consider how quickly your family will consume the menu items. Some products can sit on a shelf unopened for quite a while, but once they are opened, they need refrigeration. Pasta sauce or canned chili are good examples of this. Both require refrigeration once opened. It would be better for me to buy meal-sized jars of pasta sauce and chili rather than gallon-sized cans.