With the Prime Key you can open the Prime Crate and choose one item from its rewards.

With the Crimson Key you can open the Crimson Crate and choose one item from its rewards.

With the Gold Key you can open the Gold Crate and choose one item from its rewards.

With the Amethyst Key you can open the Amethyst Crate and choose one item from its rewards.

Gold Key Bundle contains 5 Gold Keys, which can be used to open Gold Crates and select one item from each crate.