Basically, the Social Darwinists would not have approved of any measures that were meant to help the poor or workers. They would have felt that such measures only helped those who were less "fit."
The two clearest examples of such actions by the government would be President Roosevelt's actions to support unions and to break up monopolies. Social Darwinists would have seen unions as attempts by the less fit to conspire against those who were more fit. They would have seen monopolies as the inevitable and proper result of a Darwinian competition for survival. Therefore, they would have opposed Roosevelt's progressive policies.