Back when I was having trouble with overeating at restaurants due to a similar "clean your plate" mentality, I got in the habit of just packing a Tupperware with me. When the food came, I'd pack up half of it and stick it under my chair before I started eating.

A bit gauche, I realize, but better that than overeating. Rather striking to have such a concrete illustration that restaurants were giving me fully twice as much food as I really needed to be eating, too.