Drinks
The dollar store offers a liter of soda for a buck, but you can get two for a dollar at the grocery store. If you are eager to save more, you might as well go to the local store and buy in bulk.
Pet Food
It is not worth sacrificing quality for savings when you are buying pet food. After all, dollar store pet food might not have the best ingredients. National chains also offer a huge discount if you get them in bulk.