The order in which the food is selected does not matter.
For a three item lunch, how many items are there to choose from and how many are you going to select?
Now find how many lunches of two items can be selected.
2 · 6C2
Now find how many lunches of one item can be selected.
6C3 + 2 · 6C2 + 6C1 = 20 + 2(15) + 6 = 56