Hire bikes and cycle buggies from A Bicyclette down near the beach.
The main bus stops are in Carnac-Ville, outside the police station on rue St-Cornély, and in Carnac-Plage, beside the tourist office. TIM runs a daily bus (line 1) to Auray (30 minutes), Vannes (80 minutes) and Quiberon (30 minutes).
The nearest useful train station is in Auray, 12km to the northeast. SNCF has an office in the tourist office where you can buy advance tickets.