I care a cucumber if you’re ready or not, I’m leaving!
Oh, I think I just translated that into English:
In Spanish we literally say that we care a cucumber if we don’t care at all about something.
Do you know any other ways to say you don’t care in Spanish?
Aquí las cosas “nos importan un comino o un rábano” 
We also use the phrases @SKrausser mentioned. Another equivalent could be “vale huevo” (costs egg?). Which meaning might be something like “it doesn’t matter”. For example, “me vale huevo que no estés listo, me voy.”
But, I think there is another expression with egg that is totally opposed “valer un huevo”.
We also say other things that are not so polite with “me importa un…”
In Mexican Spanish there are many ways to say this, but the one I hear most is quite vulgar… “Me vale v****” 
I’ve heard some people shorten this to a non-vulgar version, and they just say: “Me vale.”
En Colombia diriamos “me importa un carajo, o me importa un c***” jaja 
Me vale Cacahuate
Más grosero: me vale madre
Hahahaha
En Colombia también decimos "me importa un bledo". Es curioso porque un bledo es una planta 
, pero nosotros usamos esta palabra para decir que algo no nos importa o que nos importa muy poco.
