Always shop from a list and be sure to stick to it!
Really, you can save some major cash just by sticking a list. Here's a really simple example of how planning ahead and making a shopping list can save you big money.
Say you have a habit of picking up a bottle of soda at $1.25 a day from a convenience store. Those sodas can add up to $6.25 a week, $25 a month or $300 a year. Now, that may not seem like a lot at the time, but you can purchase them from the grocery store on sale for 4 pkgs. for $12 that comes out to $3 for a 6-pack of sodas. It could save you $144 a year. Think about all the ways you could spend that extra $144, and I'm not even asking you to quit drinking your sodas.
Little changes add up to a lot over time.