I'll start with a category I'll call "staples," which are items in your household that you know you use regularly and are going to keep using for the long term. If you have an ongoing expense like this, it would be crazy to not try to make it as low as possible, wouldn't you agree? Here is my list of "standards." If you have any to add or get something for cheaper somewhere, I am all ears!
1. Dog food, part 1. We feed our dog Science Diet for Sensitive Stomachs. I've found the best price for this (in California, at least) is at Centinela Feed & Pet Supply, where they also will let you sign up for coupons that make the food even cheaper. Another alternative is to go get the Sunday L.A. Times, because they have a flier in there every weekend.
2. Dog food, part 2. Our dog takes a vitamin powder called Nupro that is $20 for a one-pound jar if you buy it at the vet. After doing a little research, I realized that I could get the same product for $26.99 for FIVE POUNDS by ordering it online at DoggieFood.com. In case you don't have a calculator handy, that's about a 72% savings right off the top.
3. Vitamins. Speaking of vitamins, they are expensive if you buy them only when you need them, at whatever store you go to. I would recommend buying several months' worth at iHerb.com, where they have amazing deals and really fast shipping.
4. Groceries. I will talk more about this at length, but we try to go to Trader Joe's whenever possible. I'm not sure how they manage this, but they have the highest-quality, lowest-priced food in every city I've ever lived in.