Just so this doesn't turn into a completely religious bashing thread, I used to give up stuff like junk food when I was young. I think I gave up TV one year I was felling particularly devout.
Giving up stuff isn't a bad thing even if you aren't religious. It's good for character too. And helps make you stronger. And of course it isn't all just related to Christianity, it's a common theme in many philosophies from Buddhism to Fight Clubism...
Maybe I will give up something this year.