My Walmart pm's they post the grocery ads and usually you just tell them what the correct price is. It takes like 2 seconds and a couple of key strokes to pm. Here, the cashiers automatically pm milk, b/c they are the highest in town, so all of the cashiers know when its on sale somewhere else. If its a really rare thing I take the sales add in, but usually when I make my grocery list I just write off to the side what the price is at the other stores, then just tell them as I go through the line. I've actually had women pull out a pen and paper and write down prices as I was telling the cashiers. I've even had cashiers write the prices down as well for themselves. Afterall, they have to buy groceries or whatever too.
Also, if its a store brand thats on sale, my WM will price match it with their store brand (Great Value, Equate etc.) And, if you have coupons you can still use them along with your price match.
I actually save about $100.00 a month by doing this, and its a lot less hassle than shuffling the kids from store to store.