The word leftovers depends on having had enough to begin with.

Leftovers presuppose a surplus, and the word carries that assumption so lightly that it is easy to forget it is there. To have food left over is already to have had enough, which is not universal and has not always been true for the people using the word casually.

This is not a reason for guilt, which changes very little. It is a reason for accuracy about what your ordinary vocabulary assumes. Notice a few of these words in a week: leftovers, spare room, free time, extra. Each one marks a place where you have a margin. Knowing where your margins are is the first step to being useful with them.