I have heard the following dialogue in the TV series Marseille:
- Mayor: Regarde sus ses listes s'il y a pas un candidat qui habite hors de Marseille.
- Advisor: Il y a Godzale. Il a sa boîte mais il est domicilié à Aix. (...)
- Advisor: On se garde le coup, on verra si on s'en sert.
Context: The current mayor of Marseille is trying to be reelected and he has just gone to the second round of the elections with another candidate. He's discussing the beginning of the second round with an advisor and they have the dialogue above.
I don't quite understand this system of lists in France municipal elections, but it's clear to me the mayor wants to use some loophole in the election system and the help of someone who is registered in Marseille, but does not live there to get more votes.
What I don't understand is the expression "se garder le coup". What does it mean here? Literally, it means "to keep the blow/knock/shot" (just some of the many meanings of "coup"), but that does not make sense. The English subtitle says "to bear that in mind", but I'd like to confirm that is what the expression mean and understand better what is the underlying idea. I have searched it in WR and Larousse dictionaries and haven't found anything.