How food works in Witcher 3 combat
Food and drink in The Witcher 3 regenerate Vitality over time rather than in a lump, which makes them the cheap way to heal between fights and a poor way to survive inside one. Each item lists how much it restores per second and for how long.
One food and one drink can run at once, so the pair is worth carrying rather than a stack of the same thing. Taking a second item of the same kind replaces the effect instead of adding to it.
Where to stock up on food in The Witcher 3
Innkeepers are the reliable source in The Witcher 3, and they restock. Food is also the most common thing in containers across every region, so a full satchel usually costs nothing but the time spent looting.
Alcohol is worth separating from the rest: it heals badly but refills every potion and bomb during meditation, which is covered on the Witcher 3 alchemy page.