All three of the others you originally receive from the mail as items in your inventory. You then use the item to gain the barding, mount, or minion. (In doing so, the item itself is used up, removing it from your inventory.) Once you've used the items, you'll have the following:

Baby behemoth minion: This should be available in the Minions section of the Actions/Traits window.

Coeurl mount: You cannot actually call your coeurl yet. (You'll get an "unavailable" error if you try.) But you should see it listed under the Mounts section of the Actions/Traits window. Once you get a chocobo, doing so unlocks access to mounts, so then your coeurl will be available for use as well.

Chocobo barding: I don't think there is any way to see this until you have a chocobo. After you have a chocobo, there's a section at the bottom of the Mounts window that lets you select which barding you want your chocobo to use.