Rabeinu Yonah discusses one of the ways of repentance as leaving a little food over after the meal.
אך בעת מאכלו ועודנו תאב לאכול יניח ממנו לכבוד הבורא מתאוותיו, ואל יאכל כפי תאוותו. ודרך זה ימנענו מחטוא, ויזכרנו אהבת הבורא יותר מתענית אחד בשבוע. כי זה בכל יום תמיד מדי אכלו ומדי שתייתו יניח מתאוותו לכבוד הבורא
It seems to me the context he intended was a meal where one would save the food for a later date. My question regards how this practice could be observed in a situation where one could not save the food. Perhaps one receives stipend food in a context where saving is not an option. (Office, army, hospital etc.) wWould Rabeinu Yonah then rather wasting of food or fulfilling this edict? Or perhaps only to fulfill it when saving is an option - what if it never becomes an option (and I am too weak to fast, but I want to overcome my desires of food etc.)?