I make a menu for the upcoming week. Take inventory of pantry, freezer, etc., add any ingredient needed to itemized list. I usually shop at one store,so I have grocery list divided by isle, and note on list if I have a coupon. I stay exclusively to my list unless the store is offering specials.
I buy milk in gallons, then freeze. You have to pour a bit off the top so the containers don't burst, but just use a pitcher. When I am going to need a new milk, I just take out of freezer, put in fridge, it will thaw in a day or two. Use as usually would.