The Ready action states:
Then, you choose the action you will take in response to that trigger...
I am unsure whether this means you can only ready an action such as Dodge, Hide, Attack, Cast A Spell, or if this also includes bonus actions and reactions as the PHB states (page 189):
Certain special abilities, spells, and situations allow you to take a special action called a reaction.
And then later states (page 190):
Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.
I am aware that the Ready action uses up your action just like Dodge, Hide, and others, but am wondering whether what you spend your reaction to do can be something that would normally require a bonus action.
I am also aware that you cannot take a bonus action when it is not your own turn. Given that, one reason you might want to do this is to effectively use two bonus actions on a single turn (one using your bonus action, and another using the Ready action where the trigger occurs on that same turn).
One example of when you may want to do this (however there could be others which are entirely different in structure or setup):
You have already cast a spell such as spiritual weapon which you can use your bonus action to do something with (in this case make the weapon move and attack).
You take the Ready action to Ready the following: "When I say 'Go!', I will use my reaction to make the spiritual weapon move and make an attack."
You say "Go!", providing the trigger which allows you to spend your reaction to make the spiritual weapon attack.
You now still have a bonus action you haven't spent and can use it on anything, such as casting the spell misty step
Another possible example scenario:
You are walking past a row of allies but one is secretly an enemy and will attack you with an opportunity attack as you walk past.
You want to know who this enemy is but also do not want to get attacked.
Disengaging will prevent you from learning who they are as no opportunity attack will be provoked.
Instead you decide to Ready misty step so that "When a creature attacks me (but before they have hit me) I will cast misty step and get away" thus allowing you to learn who they are and prevent the attack.
Can you ready a bonus action?