"The jar of flour will not be used up and the jug of oil will not run dry until the day the Lord gives rain on the land." 1 Kings 17:14
At what point do you have so little that you stop giving to God? That's the point where God will demonstrate the futility of your plan because he has greater plans for His people than their self-preserving instincts will allow. Our hour of greatest need is His hour of greatest supply.