It doesn't have to be food- just something they want. If you are going grocery shopping, and your children are old enough, make them feel part of the process. Show them your list. Be sure that they have something special on the list for themselves. If you use coupons , have a time when you cut them out together.
Children love to cut out things.
They can also help you file them. If the store is a bit of a drive- make up food games to play on the way . Use your creativity. Make a game out of reviewing the food groups, and which food is in which group. Name a food group, and then give them a word which rhymes with one of the items in that group and have them guess.