Is everything good we enjoy a matter of grace?
Yes. Everything good people enjoy is a matter of grace, not deserved entitlement. The context extends grace from Christ's sacrificial death to daily blessings such as breath, food, and every good thing. A nation's abundance and standard of living are likewise portrayed as God's unmerited favor, poured out though not deserved.
Les teaches that grace is first seen in the triune God: the God of creation, one of the persons of that triune God, stepped out and took on human flesh, walked among sinful men, subjected Himself to their desires, and let them nail Him to a Roman cross. He permitted it, though He could have zapped the whole Roman empire with one word. Of His own volition He suffered and died because He was ready to pour out salvation to the whole human race. That is grace. Les then takes it further: in our beloved nation, with the last 200 years of Christian heritage, we enjoy a standard of living like no other people in human history. That too is grace; we do not deserve it. Just because we are Americans is no reason we have the right to enjoy 90% of the world's resources with 6% of its people. But God has seen fit in His grace to pour it out upon us. So everything you and I enjoy—every breath of air, every bite of food, every good thing—is grace. We do not deserve it.