PriceMatcherz is the best way to get a overview of what is on sale at the grocers in the area. You just put in your zip code, and they show the main things that are on sale at every grocer, including Target, CVS and Walgreens. It’s really good, I use it all the time.
You can also take your local ads, or online sales flyers out to Walmart, and they will match the price. I find this can save time, if it is convenient to get to WalMart. Works good.