Baby food. I'm serious! When I wore braces (from age 8 to age 15, thankyouverymuch), every time they were adjusted I could not stand the slightest pressure on my teeth. So, for the first few days, I ate baby food! It comes in a surprising variety of flavors, it's packed with nutrition, and best of all - no chewing is needed.

Of course, for school lunches, we transfered the contents of jars into unmarked leftover dishes. Much more discreet that way.