You may want to bring a flashlight, if you plan to stay in a hermitage. Meals are served communally at least once or twice daily. In others, food may be brought to the retreatant. Hermitage residents can often take food back to their cabins, if they don't want to be social. In others, they may be accompanied by music, prayer or readings.
Most meals are vegetarian and ample.
In some hermitage retreats, you may be required to bring your own food. It depends upon the retreat, but in most cases, participation is optional. If you choose a guided retreat, you may be required to participate in certain activities. Individual retreatants are often invited to join the community for services, yoga sessions, meditations, work or classes, but it's usually not required. It's a good idea to attend at least a few activities, however, as it will give you a fuller sense of the place, and perhaps another perspective.