I definitely agree that you cannot shop when you are hungry! I make a list, and then *when I do my big shopping* I check the sales for each store and decided where to purchase each item. Keep in mind that big shopping means I'm driving to the city about 1hour 15 minutes away, and can find bigger sales. It really pays to do this, and to shop around and see who has the lowest prices and best deals. Checking online sites helps me plan my trip in advance. This is usually an all day ordeal!
I make a list and I stick to it. Because I break it down by store, I only take in my list for that particular store. I get in, get the things on my list, and get out. Less temptation to spend extra that way.
Buy extra if there is a big sale. No, you might not really need 25 cans of corn this week, but if you can get it on sale and with a coupon for .10 a can where it's normally .79 cents a can, you are saving money in the long run and now you won't have to buy more for a while. (Just an example. I made up those amounts. lol)
If possible, leave the kids home with Dad or at a sitters. It much less stressful that way, and you are less likely to buy extra. (I'm sure we've all experienced the "Momma can I PUH-LEASE just have one thing?!" that grates on our nerves while shopping with kids. And if not, trust me.....YOU WILL! lol) Besides, you can be more focused on comparing prices and getting the best deal if you aren't saying "stand still" "sit still" "don't touch that" "stop hitting your brother/sister" type things every 2 seconds.