#1 had to be my biggest turn off when I was in school and going to Career Fairs. If a company was going to waste my time that could be better spent talking to someone else who was actually looking to screen and interview students either the next day or the weeks ahead then I didn't want to work for them. Usually I wouldn't even apply online afterwards. My school was always really good about getting the word out for jobs posted online so when I ran into a company just promoting their website at a Career Fair it just made me mad. Your mileage may vary...

I also completely agree with #3 too. Pick a project that to discuss that is in line with your interests and, if possible, relatively unique. Talking about the standard 3rd year electronics project, or whatever, that all EE students have to complete isn't going to stand out on a resume.

With regards to #4 all bets are off a company is giving away candy. Stock up!

I'd go into more detail but I can already feel the makings of a blog post when I get back

When you interview with a prospective employer, most employers assume you have enough brains to get a degree, so don't explain in minute detail every aspect of a project. Pick something you think presents you well and describe your role in one project. As an example, if you were a group leader for a project and you think you did a very good job setting meetings, working together, and not working to the last minute, say that and describe how you made that happen. If you think you designed some widget incredibly well for a class, describe the approach you used and something that led you in the right direction, or some particular technique you used. The point here is less to showcase your breadth of knowledge, and more to give an impression of how you go about solving problems and how you work with people. Most of the information employers look for is on your resume in the form of test scores, grades, etc. (you can debate later whether that's an intelligent practice, but that's not the subject at hand). Interviews are really more about them understanding your behaviors and attitudes.

Asking what people are looking for is fine. Employers don't want to waste their time either. Any smart employer will give very direct answers to very direct questions. If you ask and they say something vague in response, they probably aren't the ones making any sort of hiring decision and they're just a warm body sent by the company to collect resumes and tell people to apply online. That isn't to say that online applications are terrible, but your time at a career fair is in short supply; you can apply online later, just take a note to yourself if you see a company you like and want to apply to when you get home.

Last, employers don't want to talk to you and have you agree with them and kiss up for the whole interview. Just speak your mind and try to look/act/be as comfortable as you can. A little confidence and willingness to argue a point with a recruiter goes a long way. Which isn't to say you should find ways to argue, but don't just nod your head the whole way through.