Most of the destinations can be reached on foot or by metro. If you're traveling to Cape Sounion, renting a car or hiring a taxi is recommended due to the distance (approximately 70 km) from Athens.
If you have more time, consider taking a day trip to Delphi to visit the ancient site and the museum. If you're short on time, consider skipping the National Archaeological Museum, or spending less time in Cape Sounion.