The Canon E-185 Lens Cap is the replacement lens cap/cover for the EF 600mm f/4L IS USM lens.
Lens hoods are primarily designed to prevent unwanted stray light from entering the lens by extending and shading the end of the lens. In addition, since the end of the lens is extended, you also get the added benefit of some extra protection from accidental impact.
Dedicated lens hoods are designed to match the specific focal length of the lens it was designed for.
The Canon Lens Case 600 is a hard trunk case which is a replacement for the case originally supplied with the Canon EF 600mm f/4.0L IS USM Lens. It space for the lens and its included accessories.