If you go shopping while you're hungry you are wasting a ton of money and buying a lot of bad food.
According to the research you are likely to buy about 18% more food in general if you shop while you are hungry. In addition, you will purchase about 30% more junk food than your normally would too.
The research suggests having a quick snack before you go shopping. This will fill your belly with enough to not be hungry. However, you might not get what you need if you go shopping on a full stomach.
The study also says that shopping right after lunch (if possible) also limited the amount of bad foods that were purchased.