Hi Liam
What I do depends on what I'm drinking. If it is something quite young
and vibrant, I will just pop the cork back in and leave it on the bench
(or in the fridge for whites). I work in an international hotel and do
this regularly with wine samples to see how these wine will develop
when we pour them by the glass. If I am opening a bottle that has some
age on it (private stuff most often) and I know I won't drink it all
then I will pour off into smaller bottles and re seal. I always have a
few of the 187ml screw cap mini bar wine bottles kicking around for
this eventuality. I open the bottle in question, decant and fill 1 (or
2) of the small bottles to the very brim, screw the cap back on tightly
and pop in the fridge. It's also important to bring the wine back to a
decent drinking temperature before drinking.
Cheers Andrew