Is it useful to practice intoxicated? I am aware that drinking is against the fifth precept, but there are certain occasions where I can enjoy a few drinks (few times a month). I read a lot that it is not recommended to meditate purposely on any drug - but what if I did take a few drinks, should I still meditate (e.g. Vipassana) or should I skip it?
I would skip it, allow me to explain why.

Just a little bit of context:
Your question touches on a very important point about meditation currently many people see meditation as a simple tool for relaxation, some mix meditation with music, some use it for healthy benefits only, stress reduction etc... there is nothing wrong with that, however in Buddhism meditation is seen as something very different from that, much more powerful.

Meditation is something sacred, special, divine, that is why we prostate, that is why we are thankful for the opportunity to meditate, it is something that we should pay respect to, Buddha attained enlightenment meditating.

In a Nutshell, as a way of showing respect for the meditation process you should never do it after drinking, keep it as something pure, something special in your mind and in your routine.

PS: This is my approach, I understand people from other traditions may think differently