For foods that don't have a special food icon assigned yet, you can tap the icon placeholder on the Food Label and select one of 300+ custom icons shipped with MyNetDiary. It's always motivating to look at a nice-looking food diary!
You can use individual food groups or go into the full catalog. If you don't see the icon you want, you can tap "Return to Icon Groups..." row at the bottom, to go back and select another food group.