Back, body, and a lens.
Body should come with a viewfinder and a focusing screen—waist-level viewfinder is default and perfectly good. Prism is not necessary. Light meter is pretty much a must, and it would be a good long term investment, but to just get started you could try exposure tables, rules like Sunny 16, use a digital camera for metering, or a flash. Some prism viewfinders come with a light meter.