What happens next?

How to enjoy a night drinking with your family
Establish a night with your family.
Even if you decide the morning or afternoon of the night you want to have it, it still gives you time to get what you need. You could even play one by ear, if you have left over drinks from another occasion.
Consider what people like to drink, and also consider some snacks (crisps, crackers and dip etc are good), but this is optional, but is always best to eat something while you're drinking. Then, go and buy the items.