How do I save more money on the weekends?

I do a really good job of keeping my expenses under control during the week. I eat cheap, I don’t go out much, and I don’t make frivolous purchases. However, every Monday morning when I check my finances online, I find that I’ve spent $200—$300 on eating out and drinking with friends over the weekend. I’m a social person and I have a lot of groups of friends to keep up with, and they usually want to go to dinner or get drinks. How can I lower my weekend bills without changing my lifestyle too much?