Buy in bulk when it makes sense - examples include yeast, which is very cheap in bulk and can be stored indefinitely in the freezer; flour, which also stores long-term in the freezer; and eggs, which are often less expensive in larger packages. Also, chicken and beef soup bases work just like bouillon cubes, but can be purchased at the warehouse store for a lot less.
I never buy yeast in the packets you get at the store. Instead, I pay a few cents more and get a HUGE amount of bulk yeast. Now, when you look at the warehouse packages of 1 lb. or more, it might seem a bit daunting. I remember wondering if I would ever use that much yeast! But I learned quickly that the huge packages last indefinitely in the freezer with no negative effects. I do bake a lot, but it takes me awhile to go through them. So what I used to do was buy a two-pack at Sam's and share it with a friend - we each paid $2.xx and had enough yeast for quite a bit of baking. Nowadays, I buy it myself. As long as you store it in the freezer, you're good to go!
I also often buy my flour in 25 lb. bags at the warehouse club. I calculated the cost per pound and it's a bit cheaper than what I can buy at Aldi, plus I get bread flour instead of all-purpose flour. If you regularly buy the small 5-lb. bags of bread flour, you most definitely need to look at your bulk options!
Another way that I shop "in bulk" is buying as much as I can of a commonly-used product when it hits a great sale price. Examples might be cereal when I can get it for less than a dollar a box (combining sale and coupons), pasta at a .50 or less a pound, chicken breasts below $1.50 a pound, etc. When I see very low (loss leader)prices, I buy as much as I can afford within my budget constraints. This week I see a great price on chicken breasts, and I have calculated that I can spend $12 on chicken and stay on-budget. Last week I spent $13 on a fantastic deal on lean ground beef. I figure what I need and what that will cost, then divide what is left among the great deals so I can take advantage without breaking the bank.
Spices are something that it almost always cheaper in bulk. There is probably a place in your area that sells spices by the 1/4 lb. or larger, and I've found that it's a much better deal than most grocery store prices on the same spices. Plus, my bulk store is constantly replenishing stock, and I have no idea how long those jars have been sitting on shelves at the store.
A lot of grocery stores have bulk bins, and I know several people who swear by these. My stores don't have great deals in the few bins they offer, but I know some areas have fantastic options. Here, I've found mostly organic/natural products in the bins, and they are priced higher than their packaged counterpart on the shelf. I do occasionally buy these products, but not too often. Check your store to see what is offered in bulk and do your own comparison.
No matter how good of a deal you get, however, if you aren't going to use the product before it goes bad, you haven't saved anything. Be sure you either have good storage options in your house or that you only buy what your household will use in the time that the products are edible. If you have a lot of freezer space, you will be able to take better advantage of sales, but even if you don't, you can still do some bulk buying - you'll just have to be organized with your space.
What do you buy in bulk? Do you find deals online, too? I'd love to hear about it!!