We usually don't pack sliced apples in our school lunches for the simple reason that apples, when sliced and exposed to air, turn an unsightly shade of brown. That has changed since we tried one of the many apple-slice-saving ideas out there - soaking them in ginger ale for 10 minutes (I also hear any lemon-lime soda will also work).
This technique is also fantastic for packing shaped apple slices in your bento and easy lunchboxes. Best thing about it? Apples still taste like apples!