Make sure that you are checking unit prices. It is worth the cost of a little calculator. Keep in your purse so it's handy while grocery shopping. My grocery store shows the unit price on regularly priced items, but not the sales items.
I have run across, one too many times, bulk items that were actually more expensive than smaller-unit items. I have also seen, way too many times, sales items that were still costlier than off-brand items, as well as same brand but smaller size items.
So always check the unit price to see if you are really getting a deal or not.
If you haven't done this before, just take the price and divide by the number of ounces, or whatever unit of weight is used for that item.
This is a great math project for the kids to do. Assign the task to one of
your children. Or make a game of it and give calculators to several children and see who comes up with the answer first. Multi-tasking: school and shopping all in one - now that's thrifty!