For normal parties, I probably spend the most on food. It's pretty standard for people to bring a bottle of wine, or a six pack of beer with them, so I get enough alcohol to start things off, and have some extras in the back if needed.
If I'm hosting everything, drinks would come out as the most expensive. I can save on food with a combination of good cooking and reasonably priced ingredients, doing most of it myself rather than buying pre-made stuff, but that doesn't work well for alcohol.