That is a pertinent question. For a long time every time anything happened either good or bad, I answered that question with food. I tried to fill some sort of emptiness with excess food usually sugary food; ice cream was a favorite. Celebration = food, depression = food, guilt = food, unhappiness = food. Food was my answer for everything.
Food wasn't what I really needed though. What I really needed was a healthy balanced life - a life in balance mentally, spiritually and physically. I would often work on one of these aspects of my life and forget the others in my passion for all things mental or spiritual or physical - I would lose balance. I would often lose track of my Higher Power trying to do it all on my own. I would thrive for a while, but then lose focus or get burnt out and everything would fall apart and I would turn to food.
Now that I'm in OA my focus is on working the steps and finding and maintaining a healthy relationship with my Higher Power. I give the struggle over to Her and balance is a side effect.
So once again I ask, what do I need? I need food - there is no doubt of that, but not the way I once thought. I need food only to keep me alive and healthy, not to fill some perceived void. I need air and love and balance. I need my Higher Power. I need many things, but it all starts with balance, so that's what I strive for in my relationship with that Higher Power.