Breastfeeding and Alcohol

So today is my husband and mines 3 year anniversary. He wants to take me out for a nice dinner and then drinks with some friends. I am breastfeeding my 2 week old son. My question is, if I do drink, how many times do I need to pump before my breast milk is okay for my son? I planned on pumping before going out and pumping and dumping once we got home if I did decide to drink.