About 2L (8 cups) of coffee, sometimes with an additional Venti brewed coffee from Starbucks.
At that volume, yes it's an essential part of my life as I'm physically dependent on it (if I skip a day I get headaches & nausea).
Do I wish I drank less? I've quit several times in the past. My life was no better. I really do feel like it boosts my productivity.