Keep a Tally
One of the most important actions I take when I shop is keeping a tally. It's very simple, quick and always helps me monitor--and cut down-- my costs. By the time I get the cash register, I pretty much know my bill. Believe me, I see a difference when I don't tally my numbers--I almost ALWAYS end up spending more money.
I use a very simple system. This works great for me. However, you may have another tallying method that works better for you. It doesn't matter, really, how you tally, just so you DO it. Here's what I do:
On a sheet of paper, sometimes on my actual shopping list if I have space, I write down the cost of each item that goes in my cart. I round up to the nearest 5, so my figures are not exact, but very close. After each tally entry, I have a new amount for my bill. By the time I finish my shopping, I know the total cost within a few dollars. That's it. Quick, efficient and simple.