First of all, let me agree that you should not plan to do all your shopping at dollar stores. They rarely have decent produce or meat, and if you’re not careful you can get seriously ripped off on portion sizes and/or food quality.
That said, dollar stores have saved me ZILLIONS!!! (OK, not “zillions”… I’d be rich). A few places I always check are bread (I routinely get buns, sourdough loaves, dinner roles and other items, SAME BRAND, that would cost $3-$4 at most grocery stores), canned soups, fruit cups and applesauce cups, breakfast sausages, chorizo, canned meat (especially an off-brand spam), pasta, pizza sauce, many spices, peanuts, candy bars, toothpaste, dog supplies (poopie bags, collars, leashes, toys), party balloons (even MYLARS!), greeting cards, party supplies, school supplies, batteries and a bunch of other products, all usually for $1 each!
Yes, I have been disappointed in a few cases, but I have more often been surprised that no one in my family can tell it’s a “cheapo” dollar store item. I would seriously say I think I save at least $50 per month shopping at these stores.