One of the many ways that grocery stores make money is from product placement throughout their stores. You can often find many of the same items in different places around the store, they usually have different packaging and sometimes VERY different prices.
Here is one example with sesame seeds, which Mark and I frequently use for cooking. As you can see, you would spend $5.49 on this 2.5 oz container of Spice Island Sesame Seeds. This brand can be found in the spice aisle which is where most people are looking for them.
If you travel just 2 aisles over, you can find a larger 3.75 oz. container of sesame seeds in the section for sushi making for only $2.59! You would likely only look for sesame seeds in this aisle if you were making sushi, but for every other purpose of sesame seeds, you would go to the spice aisle and spend $5.49 instead of $2.59.
Another example that I found was on Almonds. Most people would probably look for these in the baking aisle first. And there you would find a 5 oz. bag of Diamond Almonds for $3.59.
But just the next aisle over you can find an 8 oz. bag for $3.99 (better price per oz.). You can also find these even cheaper in the bulk candy section, which would be closer to the $2.99 price point.
Some other places with marked up items in the grocery store are travel-sized items. You may sometimes pay 2x’s the amount for a travel sized item than you would an item on sale just a foot away from you.