One of the ways that I started saving money on groceries, was actually to not go into the store in the first place. I go to the grocery store only once a week.
Part of the reason for this is 'my' grocery store, or 'my HEB' as we say down here, really is in the opposite direction of where I go the other six days a week. Of course there are other grocery stores that I can and do stop in when I need one specific item, but general shopping for me only takes place once a week.
I'm quite guilty of heading into the store and picking up more than is on my list, because I see a good deal, or recognize something I'd been meaning to try. That clearly adds dollars to the total I will spend. Yes, I likely would have picked up those items as well at some point, but I would also argue that when I've taken the time to actually go to the store 'out of cycle' I want to make it worth my time and get more than just that one thing. You know, so it wasn't a 'wasted' trip.
So a challenge to you,dear reader. See if you can stretch a day or two in between the first time you think, "Hey, I should stop in for that one thing," and when you actually do it. Maybe you can even make it all the way to your regular shopping day. No harm in writing down the desired item on your list now, in fact I recommend it. See how creative you can be with what you have on hand today.