Strictly speaking, preparing the required ingredients and packing them in vacuum sealed bags forms an integral step of sous-vide cooking. Of course, you can work with zip-locked pouches, but the quality and doneness you achieve when cooking food stored in an oxygen depleted atmosphere of a vacuum sealed bag is incomparable.
In the most basic form, this can include cubes of vegetables, flat cuts of meat or slices of fish rubbed with spices and vacuum sealed in sous-vide grade plastic bags, and stored in fridge for a given amount of time.
Sometimes, it helps when the meat is seared before being vacuum sealed so as to get the Maillard reaction going. This is essentially the browning effect seen developing on the surface of the meat when cooked traditionally.