I agree with the previous answers so no need to repeat here.
I just want to additionally point out that such networking day is obviously a recruiting tool used by consulting firms. So while the atmosphere is meant to be “relaxed and informal”, don't forget that you are still being tested.
This ranges from your ability to carry conversations, the kinds of questions you ask, how you interact with different seniority levels and other candidates at the event to how you eat your meal. The HR recruiting team will usually collect feedback (e.g. consultants' impressions) on each candidate after the event.
The consultants at the event also know that each candidate will try to shine and wants to get a referral from them of course. The best way to get there, in my experience, is to be as authentic and genuine as possible while remaining professional. Give them the chance to get to know you as a person and try to refrain from dropping “pitches” that might come across as rehearsed.
On the flipside, you should also use this as your chance to “test” the firm. Do you like what you see in terms of company culture and chemistry? Can you envision working with the people you meet?
Best of luck and enjoy the experience