I'm O- so I give two units of red cells and get saline and the plasma/antibodies back. The guy at the donation site says "make sure you don't drink any alcoholic beverages for 24 hours...but you can have one if you want." He looks back to see if his manager is around and then whispers "you can have two but don't leave the house."
It's a requirement at Red Cross but it's just a recommendation at Vitalent- anyone can do anything but they have "ideal" donation types for each blood type.