As a 3rd year chemical engineering student, I've been to numerous networking events held by many different companies from different industries. There are a few things I would like to mention about these events that could help you make the most of it.
Firstly, networking events, as you might expect, are there to provide students with the opportunity to make contacts and obtain useful advice about what's expected of graduates in the field. To put it bluntly, the chances of you actually making contacts is very low, simply because there will be many students like yourself who want to get the same thing out of the event: vacation work and graduate positions. Now these professionals can't give vacation work to everyone and they won't remember the majority of the students they will meet. So the chances of you actually going to one of these things and leaving with vac work already settled in extremely low: I can tell you from experience that they'll just tell you apply through their website, which, ultimately, won't provide you with any advantage over the next applicant. Now I'm not saying that you won't make contacts: striking up a good conversation with them and showing a high interest in their company and your discipline might result in you getting a business card (if you're a Barney Stinson this'll be second nature for you). So what I'm trying to say is to not go these events purely to get vac work or make heaps of contacts.
What you should be going to these events for is to learn about the industry - learn about your profession, and what you have to do to be successful in it. For instance, I attended this mentor evening recently, run by the chemical engineering student society at UQ. There were numerous professionals there. I didn't attend to get contacts, but to learn about what is required of me to be a successful graduate, and to learn about how different companies operate in the industry. And I learnt a decent amount, such as how your GPA is the first thing companies look at, and how the coal seam gas (CSG) sector will provide thousands of jobs in the next decade or so for engineers. One of my friends learnt that he had absolutely no desire to work in the power industry!
So networking events can be very useful, so long as you attend to learn about your profession and to learn about how to successful apply yourself in a relevant industry.