I am a senior in college as well and I've found that the most successful way to impress an engineer is 1) to show enthusiasm about the company, about programming and technology in general and 2) ask well thought out questions (research the company/startup prior to the fair by reading their developer blog and ask insightful questions about the technology the company uses and the design decisions they have made). This will most definitely impress the engineer/recruiter and put your resume at the top ;)