The sanity food is incredibly useful if you're struggling to keep up. It has a 3 min CD, so you can't chain eat them, but 100 sanity every 3 min is still a lot over the course of a run. Ideally you want to eat in the starting area whenever you can since the passive sanity drain is at its lowest there. The other food buffs are fantastic too. It'll depend on your class/spec, but personally I find the health regen one to be by far the most useful since it basically makes you immortal. When you're regaining 2% health every second you can ignore most of the incoming damage and just focus on DPSing and avoiding sanity mechanics.