Question about breast feeding

So I'm going to give birth November 30th, and I'm going to be breast feeding. Well I've heard that whatever you consume, such as alcohol or drugs can be in your system then passed to your baby. Now I'm not worried about the drugs because I don't do any, but on New Years I had a party to go to and I was going to drink. Well would that be bad because I'm still going to be breastfeeding then? Now of course on that night my baby will be safe at home with my mom watching her and I will have left her enough breast milk for her. But idk if I should drink or not because I don't want any liquor in my system to pass to my baby.