A sustainable base on Mars is capable of generating its own power, sustenance and provisions.
Solar panels can generate all of the settlement's energy with only sunlight as fuel. The base will also recycle as much as they can to avoid more resources having to be sent from Earth or having to delve for more in the local air and soil.
When it comes to provisions, their independence will increase steadily, starting with their own production of oxygen and water when they land. The first four will also be carrying a device similar to a portable greenhouse, that will allow them to grow their own food.
As more astronauts start arriving it will become necessary for them to manufacture certain supplies themselves, rather than relying on Earth. Two examples are: