In a free market society, what are some things the government has to do because the market won't?

Intervene to protect the nature and the environment: government has to play an active role in preserving the nature from the industrial activities.

Protection of consumers and customers from malicious business activities.

Establishing a proper legal framework for the enterprises to operate under a healthy competition.

Establishing required antitrust laws to prevent unjust monopolies from taking over industries.

To enact labour laws and necessary regulations to regulate the labour market.