The presence of food does not make potions pointless, especially if they heal at different values. Tying food you loot and find in the world to resting means you would present a hard limit on how many times you can rest, or the food is so abundant it doesn't limit anything and is just an arbitrary requirement. The former isn't ideal because it would present the possibility that a player has used up all of their resting materials and is suddenly stuck unable to progress, and the latter is pretty self explanatory. It's an interesting idea but I don't think the problems it presents make it worth the inclusion.
Maybe all the merchants could sell food (at a high price) ? Rewarding those who take the time to loot foods, without stopping others who are lazy.
If you have no more food and killed all the merchants you really want to hurt yourself ^^
And if food is abundant, it doesn't make it useless but just more immersive in my opinion. Not to mention that it takes up space for equipment.
