This is a very commonsensical point that shouldn't need to be stated, but does when it comes to student organizing: college students like free stuff. Especially when you're starting out, advertising free food, free refreshments, free cookies, pretty much free anything will help you draw a crowd. Food is not enough, mind you, as students are evaluating the cost of attending your meeting versus the benefit of the free stuff they will get. And as time goes on, a reputation will develop of whether your group has good free stuff or bad free stuff (everyone knows which organizations order 10 pizzas for a meeting versus those that have a single bag of pretzels for everyone to share). Whenever you can, though, you should have things to give away at events, including libertarian books/magazines.
Note: Creativity is also highly valued by students. Instead of getting plain cheese pizza, go for the meat lovers and garden pizza, or even try Thai or other types of food to change it up. The small touches make all the difference.