How to consecrate food bought in a store?

Hello Marina! The consecration of food in any tradition requires attention, concentration and prayerful mood. It's good if there is a special place where you can do it. The guise of the entries is for example, some people pray before eating and thus they consecrate food. In other spiritual traditions, people put food on the altar, reading a prayer, and only after that they accept it. Here it is important to understand the essence. And the essence is that attention and prayerful mood are important. The salient also has some moments in life when there is no way to do it properly, but a person wants food to be sanctified, then prayers can be offered in the mind. But ideally, you need to pay due attention to this process, since it is necessary not for God, but first of all to us. It is our gratitude to God for what He does for us, for giving us this food.