Get a taxi in the centre of Calama. It will take you to Chuquicamata in 30 minutes.
You can walk around. Its cool because the city is almost dead now. There are some dark restaurants and strange places. Its cool to walk around but don't miss the guided tour to the mine. You cannot get into the mine by yourself as its a industrial facility operating 24x7.
Once upon a time 'Chuqui' was a real town, but now its drowning into mine rejects and nobody lives there anymore. Don't miss the guided tour to the mine. It runs every day and is totally free. They ask you for a donation. It takes an hour and you'll be able to see the mine, trucks and other mining equipment.
If you like photos, bring you "super-ultra" wide-angle lenses. Its really difficult to take a picture of the entire mine with a regular camera, a wide-angle will give you great pictures.
There is not much more to see in 'Chuqui' but get yourself some time to walk around, its worth it.
Note that as on Jan/2006 the tour was spoken only in Spanish.
There is not much to buy there. Maybe some food.
I tried to buy myself something to eat, I failed. Places are dark and driven to the miners, not to tourists. Bring something to eat and drink or good luck.
It is a hot place, bring water. You can buy something to drink there.
There are no places to sleep there, no hotels. The city is dead and nobody should stay there the night but people working in the mine.