The calorie system is to encourage managing between life and time, if you get damaged you can wait to recover a bit, but if you do so you're loosing precious calories and will need more food.
From my experience if you don't take too much damage and avoid waiting arround (and generally don't waste time) you should be largely capable of exploring floors fully without dying of hunger with the sandwitch drops.
Also if you're lucky you can get a calorie ring that allow you to gain calories via sex scenes, tho that entails cum management.