Paraxis, Rlyehable: do either of you have any specific rules text in mind, which guides your answers?
READY
Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn so that you can act later in the round using your reaction.
First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.
>You either ready an action or can choose to move up to your speed in response to the trigger, you don't get to move on a reaction and take an action.
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BONUS ACTIONS
Various class features, spells, and other abilities let you take an additional action on your turn called a bonus action.
You can take only one bonus action on your turn, so you must choose which bonus action to use when you have more than one available.
You choose when to take a bonus action during your turn, unless the bonus action’s timing is specified, and anything that deprives you of your ability to take actions also prevents you from taking a bonus action.
>Bonus actions can only happen on your turn. Now specific might trump general so possibly the charger feat allows you to get a bonus action attack when you ready a Dash action.
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There are some weird rules interactions because of these things I have noticed.
First, regarding the ready action, on your turn you could move your speed of 30', then ready the dash action to trigger on something you know is going to happen soon like an ally starts to move, and when you take the dash action you do get to move 60'.
DASH =
When you take the Dash action, you gain extra movement for the current turn. The increase equals your speed, after applying any modifiers.
That seems pretty odd to me, anyone can triple their movement essentially.
Second, since you can take only bonus actions on your turn, you can't ready a spell with a casting time of 1 bonus action.
Casting Time BONUS ACTION =
A spell cast with a bonus action is especially swift. You must use a bonus action on your turn to cast the spell, provided that you haven’t already taken a bonus action this turn.
This means you can't ready a divine word spell until the horde of enemies is within 30' of you, you can't ready a misty step spell to trigger when the moving platform comes within 30' of you, stuff like that.
So while all this is stuff is RAW, sometimes it doesn't make sense.
I don't allow the Dash action to be readied, the choice of movement is already stated as an option in the ready action. I do allow 1 bonus action spells to be readied because to me it just makes sense that you could.
I love rules, and rules lawyering and try to play as close to them as I can in most situations, but there is a reason we DM's are individual human beings and not computer programs.