As much as the heart can hold or contain; as much as a person wants or can endure. Frequently with of.

So much as will fill a person's lap.

A quantity that fills the throat; as much as the throat can hold at once. Also figurative.

A quantity or amount of something that fills or covers the breast.

As much or as many as can be held between the toes (or claws) or otherwise lifted using the foot.

So much as will fill the lungs; spec. a quantity of inhaled cigarette-smoke.