I have to admit, some days the primary reason I get out of bed is because I'm hungry and I'm addicted to cereal. I can't start my day without cereal. And if I'm out of cereal and/or milk for some reason... it's pretty hard to find a reason to emerge from my nest.
Other reasons for living... inertia. An object in motion stays in motion. An object at rest stays at rest. Unless I'm edging on serious depression (which is the "rest" part), I am usually inclined to maintain my life-momentum and just keep right on moving. Hard to explain. It just is.