tModLoader How do I make a custom "goodie bag" / "present?"

[JayStarPlays]

How do I make items drop during holidays, similar to the "goodie bag" or "present" items?
What do I need to do, and what code do I need? I already know how to make a custom treasure bag, I only need help with dropping it.

I'm specifically trying to make an "easter basket" that's like a goodie bag / present that drops in April, around Easter.