Pop-Tarts are a cheap, readily-accessible, easily-consumed source of calories with a long shelf life that most people will at least tolerate. They're nutritionally incomplete, but they will help keep you alive and functional in the short term.

Most people don't stock up on MREs and survival bars, nor even have a clue where to start. Under such circumstances, it's both expected and reasonable that they reach for a familiar, readily-available energy source.