Has anyone ever actually been to one of these? What are they really like?

A recent thread indicated that what you bring could be confiscated. I'm not talking guns & knives, but useful things like granola bars and blankets. Is this true?

How do they operate? How do they feed everyone? What do they use for toilet facilities? Water? Power?

Just an overview of what it's like is all I'm looking for. Just curious, as I am not likely to abandon my pets for some reheated macaroni & cheese and a collection of screaming kids and complaining teenagers.

Sue